Pickup chip truck
My first chip truck was a plywood box built onto a flatbed. I've evolved, but I remember the hardship of offing the chips. I began employing a series of tarps. Tarp # 1 went from the tailgate end, up to the front, then 1/4 of the way up the 'impact wall'. Against the wall I'd place a 3' x 3' square of plywood against which I'd take aim and blast chips. This first layer would get a light load of chips, mebbe 100 lb or so. Chip away, Hardman.
Remove the blast square, take 20 seconds to spread the chips to an even surface side to side, deeper in the far end, tapering shallow toward the tailgate. This is important. Also important is the blast square, without which you'll blast holes in the tarps in no time.
Enter tarp #2, laid over the chips and half way up the impact wall. Place your blast square against the back wall and continue chipping, about 150 lb this time. Same deal, remove the blast square, spread the chips out, and now you've created a wedge-shaped chip hill, higher at the wall end, sloping downward to the tailgate. Enter tarp #3.
Onto this level you can chip a few hundred pounds because if you're following the pattern, when it comes time to off the individual tarp layers, the higher-up ones will be sliding downhill and can be substantially heavier than the bottom ones .
You'll max out at 4 or 5 tarps, but when it comes time to offload, the topmost, heaviest ones will come off easiest. It's a PITA to crawl in and out of the back end of the truck, futzing with tarps, and interrupting your chipping session, but its worth the magic in pulling off an entire truckload of chips in mere minutes at the end of a long day.
I'm glad to have moved beyond this method, but it worked really, really well for the time. TIP: Screw some small spring clips to the blast wall to attach the ends of the tarps. They'll self-release when you do your pull-offs. -TM-