I tightened down and cleaned up the negative battery terminal, that seemed to solve the intermittent warning light issue.
I then undercoated the entire truck with 3M Cavity Wax, including inside frame rails, underneath bed, etc. Works really well and applies easily, I prefer it to products like fluid film.
Did some light off-roading with friends, the truck did well! I loved putting it in 4H, 1st gear, and turning up the idle knob so it would creep along. The heater is miraculously still working, no leaks.