A typical uni-body car is most than strong enough for the weight, but there is likely no place where the sheet metal is strong enough to support the bolt. You can make it work if you want, but it requires a more complex mounting system. (of course a truck has a nice open bed which has other advantages for mounting a gun - the typical car doesn't have a good place to mount the gun even if you build the mounting system).
ATVs can carry the weight, but finding a place to put the bolts will be a pain.