Adam,
There is nothing wrong with making whatever vehicle you like and painting it however you like, but I wouldn't want to go to a Military Vehicle show and see a load of dune buggies painted nato green. (Unless they are ex-military dune buggies of course) If I go to a military vehicle show I want to see military vehicles, I want to see them as they were in service, not pimped up with any and every accessory the owner has been able to buy at the stalls. I understand that many of the older vehicles have spent longer in civilian usage than they did in service, and that as long as they are on the roads and going to shows that's fine, but I've been to a number of shows (W&P is the worst) where anything with vaguely military markings is put on display, and I don't think that should be happening!
Chris