I have some notes somewhere regarding 3point vs 4point mounts from when Eddie built my camper mog.
A mog typically has a spider frame which 3 point mounts to the frame and gives a rigid platform which you can use for whatever. Initially my box was going to be put on this spider frame but the platform is about 8 inches higher than it needs to be. Eddie was a mechanical engineer and decided to mount camper shell directly to the frame to get the center of gravity that much lower, this is pretty much what unicat and those folks do but I don't know how they decide where to put their mounts.
He ultimately decided on a 4 point mount which is rigid in the center and pivoted at front and back. He did a load of tests figuring out where to put the pivots, weather to use 3 or 4 points and where to place the center bar. His reason for moving the pivots around was to find the place that had the least movement in the pivots so he never exceeded them and stressed the box. This is very specific to how a mog frame, specifically a long wheel base 416 and the info may not be applicable to anything else, regardless I'll dig it out and share it.
When emailing with him at the weekend I as how much thought he put into the reverse problem of the load stressing the frame/truck. He generally put no thought in to because he was under gross weight and the mogs GVW rating is for an absolute worst case scenario, something 20 degrees of frame twist, off camber, 45 degree hill, locked diffs with a single traction wheel. The only thing he did to the frame was to modify the front cross member as its a common place for a 416 frame to break due to the engine, the suspension mount and the power steering all being in the same area.
Eddie never had frame problems but he had a number of drive line problems. He bust two sets of portals before Mercedes realized what the problem was. It was related to the disk brake trucks having the same GVW as the drum brake trucks but the disk brake trucks have about a 5 inch spacer to clear the caliper and rotors. At gross weight in bad conditions this puts a huge amount of stress on the final drive bearing in the hub. The final solution was to use 1300L bearings, the 1300 uses the same hub casting as the 416 but they use 13mm roller bearings instead of the 9mm in the 416. The 1300 also has a higher gross weight than the 416. You put a bigger bearing in the same sized hole and you then need smaller portal gears and the 1300 gears are a different ratio to the 416 so he had to replace all 4 hubs. Fortunately Mercedes paid for it as long as he returned all the failed parts to them, that would have probably been a $15k repair. Since this repair Eddie did another 100,000 miles over many years and I have put 25000 miles on it and never had a problem.
I don't think huge mechanical failures are uncommon, even the mighty unimog can fail in some spectacular way that has never seen before.
One thing I would ask Mitsubishi is how they derive the gross weight of the frame? Is it based on loading, braking, twisting etc? Does it factor in 4wd situations or was the fuso 4wd more of an after thought, is the 4wd made for what its being used for or was it more intended for making deliveries in snow. Without knowing this Doug's truck could be way way over gross weight for the scenario.
I'll dig out and scan all the notes and experiments and post them up.
Rob