If it is like My Silver Streak--I would say either:
1. see if you can re-adhere the panles to the wood substrate OR
2. it is probably an 1/8th inch(5/32) luan and that is readily available at lumber yards
This is what was used on the facing of cabinets and walls on mine...originally it had a laminated(?) wood grain...
Kinda depends on what You would like to see happen with the walls?
As for the remainder of the original walls on mine(that aren't painted)...I have decided to sand the original finish off and apply a satin poly over the natural wood(luan) facing.
This is what I did for the cabinets drawers and doors in the kitchen area to compliment the painted areas on My '77 Silver Streak "Refurbish".
Logic, Reasoning and Cost Happening....All Part of the Visualization--Not a Rationalization...