My personal opinion is that if you model military scenes, sooner or later you'll need to model a casualty or three.. The trick is to keep it real, and not splash bright red paint all over the place, which quickly arks you a tasteless amature... Keep the gore to a minumum and you'll do just fine.. Unless your real intent is to shock your viewers, that is... Just keep in mind a could of things.. Dead men don't bleed (the heart has stopped), and with gunshot wounds, have the blood running from them in fine lines on the skin, not big ol' blotches, and if your casualty lived for a bit before bleeding out, and didn't have an exit wound, most of the bleeding would be internal...
To effectively model a gas casualty, I'd put a pro-mask in his hand or lying next to him on the ground.. That'll tip your viewers off with having to do a lot of explaining... Depending on the era you're modeling, you could even add period NBC contamination markers... The "GAS" and "GAS MINES" signs are particularly effective in late 20th century and today...
Like AJ said, an for an effective diorama, the viewers should immediately know what's going on without a title or story to read..