I did a bit of checking around. www.imcdb.com (internet movie car database) has no record of Battletruck or it's alternate title Warlords of the 21st Century. Also no joy on a Google image search. My advice is to watch the movie, see if you can't spot a badge or something to tell you the make of the truck. In any case, I would then check Ebay for a truck of that make or at least one that looks similar. Start there. As for modifications, check your LHS for scale diamond plate, round/square tubing. Use household items to replicate features. I had a friend that made fuel tanks for a post-apoc build using cigar tubes.
Also, another idea for identifying the truck is to check the truck forum at www.scaleautomag.com, it's another Kalmbach title,so its cool. Those guys might be able to help you, because they are serious car/truck guys. Let us know how it goes.