One of the guys I play with has an Iltis which is registered for the road and strictly for the "cool" factor, so it doesn't see real action.
With that said, we also have a Chevy Blazer that is, shall we say, "modified".
It got the back cut off so more people can jump in and out more comfortably, massive I-beam bumper, and painted a nice OD.
As far as rules, it usually operates in is limited to the open fields around the bush of our AO, however we do have a "road" that it will go along through the bush.
Common sense is the main rule regarding it.( no hiding in long grass where it may be comming)
also the muffler fell off awhile ago, so you really can't help hearing it coming towards you(that and the loudspeaker system)
As far as "killing" it, we have an AT-1 that runs off compressed air and fires dollar store foam rockets( or anything else you care to stick into it). Usually there are enough people around to see if it gets hit or not. Generally the blazer is considered immune to gunfire with the exception of if there are 2 or more players and the blazer is not escorted. In this case it would also be "captured." This keeps the driver from merely roaring up and down the path with no escort team and giggling to themselves.
and paperwork, well, we play on a private field that also is where it is stored. So unitll we look into taking it to some of the "larger" games, its not really an issue.
I have to admit tho, its intimidating to see "something" full of people with guns, roaring over the crest of a hill, blaring "ride of the Valkyries", with the driver yelling obscenities over the loudspeaker.