My $0.02 worth: That is a big and relatively heavy trailer and between the possible paint issues, 24 volt electrics and all the structural mods you want to do as well as the overall "beef" of it I'd think you'd have much better luck building from scratch or modifying a "Little Guy" tear drop for off road use or even converting an older tent trailer.
As for the solar generation, this is something I have experience with. I have solar in my trailer, on my tow rig, on our boat and we have an entire solar powered cabin. Putting together a system to suit your needs from parts is sooooooo much cheaper and flexible than buying it all together. I just priced out a simple Titan system and the cost came up to more than we spent to equip our off grid cabin to run all the normal appliances like washer/dryer/dishwasher/gas furnace/etc. We have lead-acid batteries but the last set lasted 12 years before needing to be replaced, Titan rates the lithium pack in their unit as a 10 year life span. There are tons of online resources for building solar now, that makes it pretty easy. Good luck with your build!