Three modifications come to mind as my favorites.
Frontrunner water tank. This tank was a serious game changer for my annual trips. Having 10 gallons of fresh cool water easily available has been incredible.
Rear door table. This table is a spin off from the table I built for my old Disco which was inspired by the Olivares table(s). I used kitchen grade stainless, 10lb gas struts, and bamboo for the table. This is used constantly on my trips and is great for quick lunch stops or for camp cooking.
Rear storage/ sleeping platform. I decided to build a flat platform that I could sleep on but I also needed storage for spares. In addition, I wanted a drawer for kitchen goods and an open cavity for storing other camp items like; camp table, snow peak grill/ fireplace, axe, charcoal etc. Random stuff. The front of the platform is accessed/ divided through two boat deck hatches. These compartments are low and center and house all my heavy spares and other tools that I don't readily need. They mount flat and aren't an issue at all to sleep on.