As long as the box is constructed properly, it's purely for looks. (it's amazing what kind of box construction sins can be covered by carpet...)
I reckon being that this box is for a ute, just a few good coats of some kind of sealer (oil based undercoat would work fine) so it doesn't absorb moisture and you'll be good to go.
Best of luck!
__________________
.
New look ASR Website online now!!
www.asr-audio.com.au
Interior lighting and audio specialties
for VT/VX & VY/VZ Commodore / Monaro
Click the scales if you like - or not - what I have to say...