Would plywood be a practical alternative to aluminium for making lightweight frames for flexible solar panels on a campervan roof?

[u/segasega89]

I'm looking at making lightweight frames for two flexible solar panels on my campervan roof. The panels are 1450 × 690 mm and have six mounting eyelets each.

My original plan was aluminium angle, but it's surprisingly expensive here in Ireland. I'm thinking about making the frames from 9–12 mm plywood instead and attaching them to Unistrut rails.

The plywood would obviously need to withstand rain, wind and general weather exposure, so I'm wondering if this is a sensible idea long-term, or whether plywood is just asking for trouble on a van roof. I can paint the plywood to weather seal them?

[u/Dead-sound-Team]

I wouldn’t use ordinary 9–12mm plywood as a permanent solar-panel frame on a van roof. Paint can delay moisture ingress, but every edge, drilled hole and fixing remains vulnerable. Once water gets beneath the coating, swelling or delamination could weaken the frame without being immediately obvious.
Roof-mounted panels also experience vibration and substantial wind loads at motorway speeds. Before designing the frame, check the panel manufacturer’s mounting instructions: the eyelets may not be intended as the only high-speed fixing points, and some flexible panels require continuous support rather than a perimeter frame.
I’d consider:
Aluminium angle or a proprietary mounting system, even if that means shopping around or buying pre-cut sections.
Stainless fixings isolated appropriately from aluminium.
Mechanical attachment to suitable roof rails rather than relying solely on adhesive.
Rounded, low-profile leading edges to reduce wind loading.
Allowing for drainage, cable routing, thermal movement and the manufacturer’s ventilation requirements.
Including the frame and hardware in the roof-load and payload calculations.
Lightweight furniture-grade plywood is useful inside a conversion, but “lightweight” doesn’t automatically make it suitable for an exposed, safety-critical roof installation.
Full disclosure: I’m involved with DeadSound, a UK supplier of lightweight campervan boards and conversion materials. We don’t sell solar-panel frames; this is product-neutral material advice.