I've just moved by tank back about 30mm, and there are only four bolts holding it in. The wood is fairly thick - I'd say about 15 - 20mm and there is a hole towards the back for the tank drain plug. The thickness of the wood means that the drain plug does not protude further than the wood, which would mean the wood offers it some protection.
Personally I can't see any issue with changing the material as long as it retains the same structural rigidity, there is the same protection for the drain plug and the filler hose still fits ok. Sorry, don't know what the wood is, but it is 'wood' rather than 'ply'.
