Hi atreMF
I'm fairly new to this forum too, but I've found the guys and girls here are great - so stick around.
Is the kit the Italeri "Commando Car (jeep)? If so this is supposed to represent the jeep used by the SAS in Nth West Europe and Germany (Africa having been liberated by then). As SF rightly says, consider then the uses they put it to, and what would be the result of that.
The inside of jeeps were fairly knocked about by the various types of containers and gear carried - not to mention less than careful soldiers. Boots chip paintwork and leave mud, bits of dry grass and twigs inside, or just leave dust marks at the best of time. Look at the inside of your own car, and that gets cleaned out regularly.
The fuel tanks are located inside above the rear wheels, consider fuel spillage, etc.
The SAS jeep did not appear to have a hood, so it was open to the elements. Rain would make mud and dirt run,etc - so this would run into nooks and crevasses and later dry there.
Recent use of the guns would leave spent shell cases on the floor, etc
There are a few good books out there about the SAS in WW2. If you can pick one up (or see what your local library has) you can get a feel for how they "lived" in their vehicle. This will help you get an idea of what to do.
This site is brief but has a picture of the so called "Comando car":
http://ourworld.compuserve.com/homepages/jeep_man/sasjeep.htm
There are more out there, just use your favourite browser.
Happy Modelling
Peter