Advice on making flatbed out of RV trailer chassis
Hey everyone,
I recently picked up a 1983 Peitz twin-axle camper chassis for cheap and am converting it into a flatbed trailer for general cargo. The design will feature an "over-wheels" or "wheels-outside" layout, giving me a clean, flat deck surface.
Because the entire chassis is factory zinc-plated and bolted together, welding is completely out of the question. Any new cross-members or frame extensions must be strictly bolted on.
I’m looking for suggestions on the easiest and/or lightest way to build the cross-beam network to support the deck.
Here are the exact specifications of what I’m working with:
Chassis & Axle Specs:
Axles: 2x Peitz 850 kg (1,873 lbs) steel-torsion sprung axles with Peitz overrun brakes.
Weight Ratings:
Plated for 1700 kg (3,747 lbs), but officially registered/titled for a gross weight of 1399 kg (3,084 lbs).
Wheels/Tires: Stock size is 145R12, but swapping to 145/70R13 due to modern tire availability.
Existing Steel Frame (81x50x4mm / ~3.19" x 1.97" x 0.16" C-Profile):
Cross-beams: 2 main cross-beams (front and rear), 1830mm (~72" / 6 ft) wide.
Longitudinal Beams: 3 horizontal beams running the length. The outer beams are factory-reinforced with an 80x50mm (~3.15" x 1.97") angle-iron welded to the inside, heavily reinforced around the axle mounts.
Total Planned Bed Size: 4530mm x 1520mm (~178.3" x 59.8" / approx. 14.8 ft x 5 ft).
Decking Options I’m Considering:
16mm to 21mm (~5/8" to 13/16") waterproofed/form-plywood (single sheets).
36x148mm structural timber (~1.5" x 5.8" / similar to US 2x6).
28x120mm decking boards (~1.1" x 4.7" / similar to US 5/4x5).
My Questions for the Group:
Given that I have a solid 3-beam longitudinal foundation but need to bolt everything, what profile and material would you recommend for the upper cross-members? I want to keep it light to maximize my ~1400 kg (3,084 lbs) legal gross limit, but stiff enough to support the deck. (e.g., steel C-channel, hat-channel, or heavy-wall aluminum?).
If I go with the plywood deck vs. the 36x148mm structural wood timber, how does that change my cross-member spacing? The structural timber is heavier but naturally bridges wider gaps, whereas plywood is lighter but needs tighter joist spacing to prevent sagging.
Should I bolt cross beams between existing frame or make a complete frame on top?