I know it is not a major mod or upgrade, but it is the one I appreciate the most. My toilet riser.
I have removed carpet and resurfaced floors, fixed slide mechanism, and re-balanced the slide on the rails, reinforced shower basin supports, removed dinette, couch, and queen bed, fixed and re-roofed the front 1/3 of 5er, fixed steps, fixed and painted the door, added skid proofing to the steps, replaced faucets, built beds, tables, and shelves, replaced landing gear (twice), fixed and replaced the refrigerator twice, and installed an additional 120V small refrig., replace most all of the windows, fixed both vents and added vent hoods, and fan, added 12V fans to Refrig and Refrig vent, I do my own wheel bearings, flipped the axles, replaced the voltage converter, rewired the 7 way plug (three times), removed fixed and replaced the hotwater heater and the forced air heater, made and installed my own hotwater heater bypass, installed my own rear view camera, and some other things I am forgetting......
BUT the riser is the best.
Thought I would share by favorite mod.
5er/2500Duramax/18ftBoat