Nice, lots of ideas here. For me in no particular order
Foam mattress toppers
230 watt solar charging system
1000 watt inverter with remote
Battery and solar charging monitor
Replace all bulbs with LEDs
Additional battery capacity
Tongue mounted diamond plate toolbox/battery box
Fold down countertop extension
Updated bbq with rear bumper swing arm mount
Plexiglass shower rails to keep water from spilling out
Added couple of 12v outlets as the trailer had none as delivered :(
All I'm missing is vented catalytic heater so I can ditch the power wasting furnace. Maybe soon :)