Once the insulation is in place, and you've laid the most important foundation for your warm, dry home, it's time to build the sub-frame, which is inextricably linked to the insulation. In this article, we'll cover the basics of this frame and show you simple solutions for a quick start.
Image: Steven Funk
The sub-frame isn't just for cladding the walls. It's the invisible, load-bearing framework that will later ensure your bed, wardrobe, and kitchenette stay securely in place even during a sudden stop – and nothing rattles!
Here's how to create a stable base and how you can get started right away.
1. How do I create the sub-frame as the foundation for my conversion?
The main task of the sub-frame is to create a stable connection between the new furniture and the metal bodywork without damaging the vehicle's outer shell.
Which materials are best suited for the frame?
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Birch Plywood: Although squared timber is often used, birch plywood (ideally 21 mm thick for maximum screw retention and hold) offers significantly higher stability and prevents the splintering that often occurs with solid wood. It is the more stable, albeit heavier, choice.
Important: The thickness of the chosen profiles/battens (e.g., 21 mm plywood strips) determines how much space you have behind the cladding for cables and ventilation hoses.
Why we don't drill holes?
Every unnecessary hole in the van's sheet metal is a potential rust spot. Therefore:
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Utilize factory mounting points: Whenever possible, use existing threads or holes in the bodywork bracing.
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Rivnuts as lifesavers: This is the best method to create mounting points without drilling through the outer skin. A rivnut is inserted into an existing hole in the inner sheet metal, crimped there, and provides a solid internal thread (M5, M6, etc.) into which you can simply screw your wooden battens.
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Bonding is the new screwing: Modern polyurethane adhesives (like Sika 554) are often the more stable and secure choice for connecting wood and sheet metal. They offer a permanently elastic connection that absorbs vibrations and stresses during driving – unlike rigid screw connections, which can loosen over time.
The holding power of these adhesives is enormous: a thumb-sized adhesive area already holds approx. 3.5 kg. Over one meter in length (e.g., when bonding a multiplex strip), the adhesive thus holds approx. 350 kg. Therefore, permanent elastic bonding is often superior to even the best screw connections and is the clear recommendation for load-bearing elements.
Important: For the adhesive bond to truly be this stable, the substrates must be treated according to the manufacturer's pre-treatment instructions. Depending on the material, this may involve sanding, the use of primer and/or activator in various combinations. Only a properly prepared substrate guarantees the full holding power of the adhesive.
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Where do I position my sub-frame?
Positioning is crucial. The sub-frame should preferably be bonded where the vehicle's sheet metal is most stable (e.g., at corners, folds, and solid bracing).
Two important rules of thumb:
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Reinforce load points: Primarily place the battens where your furniture, overhead cabinets, or bed frame will later be screwed. This ensures that the load is directed directly into the most stable areas of the vehicle.
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Wall cladding: Once the sub-frame is securely in place, the wall cladding can be installed. Thin panels like 4 mm multiplex (e.g., poplar or lightweight Queenply) are suitable for this.
Absolutely remember: Before attaching the wall cladding, note the exact positions (height, distance) of your sub-frame. A simple photo or sketch is worth its weight in gold, as screwing in furniture later will quickly become a guessing game otherwise.
2. What should be considered for the floor plate?
The floor is the most important reference point in the van. It serves as the foundation for everything you place on it (seats, table legs, cabinets).
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Substructure: Here too, we bond 21mm battens made of birch multiplex. Ideally where the greatest load is expected. Under the furniture, the entrance, and walkways. Good insulation will be installed in between.
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Floor plate: Use a stable, moisture-resistant board, e.g., a 9 mm or 12 mm multiplex board or a screen printing plate. There are also special floor plates that have an additional cork layer in the middle. This provides additional acoustic insulation.
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Fastening: The floor plate is screwed directly onto the sub-frame. This gives you a very solid base on which you can build everything else.
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3. How to get started quickly: Provisional furniture, modules, or repurposed items?
Before you embark on the elaborate construction of fixed cabinets, you can hit the road immediately with simple, provisional solutions. This gives you time to learn your ideal routines and measurements in real camper life.
Which simple solutions and items can I repurpose?
Instead of sawing wood and building cabinets, you can repurpose everyday items:
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The bed system: A folding slatted frame or simply a high-quality, thick sleeping mat or a rubber mat on the floor will suffice for the first few nights. Alternatively, sturdy stacking boxes can serve as a base for a folding mattress.
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Storage & kitchen base (Euroboxes): Sturdy plastic crates (Euroboxes, IKEA boxes, or even beer crates) are your best friend. They serve as stackable cabinets, a cooking surface, and can even be used as a provisional bench.
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Table & chairs: Use your camping folding table and camping chairs. In the van, these serve as a dining area or workspace and can be quickly stowed away when not in use.
Safety note: Even provisional items MUST be secured during travel! Use the existing lashing eyes in the floor of your van to strap down boxes, mattresses, and folding furniture with tension belts so they don't become projectiles in a sudden stop.
Are modular kits an alternative for a quick start?
If you want to get on the road quickly or keep your conversion flexible, a ready-made modular kit is an excellent alternative to building it yourself.
Such systems (like the Boxio Rack module) often offer space-saving all-in-one solutions that already integrate the essential functions:
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Kitchen block: With sink, stove, and storage space.
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Sofa bed: Convertible seating and sleeping arrangements.
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Toilet: Integrated, removable solutions.
Your advantages: The modules are lightweight, save planning time, and can usually be installed quickly without complex sub-frames. Often, a floor mounting is sufficient. They are ideal for not letting the camper "rot in the garage" and offer the option of upgrading to a permanent conversion later, as they are reversible.
FAQ: The most frequently asked questions about sub-frames and furniture construction
1: How do I securely attach the multiplex strips? The multiplex strips are glued to the pre-treated bodywork with a strong, permanently elastic mounting adhesive (e.g., Sikaflex or Dekaseal).
2: Do I have to screw my furniture into the camper? Yes, absolutely. Anything loose in the vehicle can become a dangerous projectile in an accident. Even light cabinets must be connected to the vehicle frame via the sub-frame.
3: How do I avoid rattling/creaking noises? Use felt between all wood-to-wood connections that are not firmly glued. Where wood meets sheet metal, the insulation and adhesive ensure quiet.
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Conclusion:
The sub-frame is the most demanding and fundamental part of the entire conversion. It requires precision in adapting to the curves of the bodywork and careful pre-treatment of the adhesive surfaces to ensure the full holding power of the adhesives. But precisely because the foundation is laid here, every hour invested is worthwhile: If you work neatly, stably, and safely, you not only create a load-bearing base for all subsequent furniture. Above all, you ensure that your van remains a place of peace even after tens of thousands of kilometers on bumpy roads. Because a firm, vibration-dampening sub-frame prevents creaking noises, protects against material fatigue, and guarantees that all structures remain securely anchored – the best prerequisite for many years of carefree, rattle-free travel enjoyment.
