As with the Abrams, this build isn't quite what I'd hoped. I don't expect perfection; I lack patience and I'm not a rivet-counter. In addition, I also enjoy my builds being functional, so they're not just a static model or even a mobile RC one, but can actually *do* whatever they're supposed to do. It's that last requirement that sometimes bites me.
What I found with this build is that yes, the truck will pull 20+ pounds of trailer with 50+ pounds of tank ... on flat ground, with traction. To aid with traction, I welded up some scrap steel to put inside the frame, adding weight over the axles (about 4 pounds over #3 and #4, and about 6 pounds over #2.) That helped some, but it also made the driveshafts pop out, doh. Also, as mentioned, when loaded, tight turns make the trailer tires start to dismount, ugh.
The truck itself came out pretty well, though, and I'm pleased with some of the parts being close to the 1:1 AND being functional (the bogies, for instance, are simple, but look mostly right and are strong enough to hold up, well, anything.) The trailer steering is actually great fun to watch, as the Arduino does its scaling magic. It's harder to drive than a regular trailer because it slides sideways due to the active steering; I'm used to trailers being passive and just following the truck. The HET's rear having the reversed steer also means you can jack-knife the thing in a heartbeat. My lovely wife is very understanding, but even she got tired of me testing the apparatus in the hallway and banished me outside.
I can say I learned a lot; my OpenSCAD skills are definitely improving, I can plastic-fab stuff with some expectation of positive results, and overall I had fun. Which I suppose is the important thing. Just wish the dang tank wasn't so heavy, and geared better, and ... =))