Can't comment on what products do or don't work on the decals, but I know not putting anything on them will make them peel and fade after about 10 years... ;)
Well, they actually started a lot sooner than that.. It was at the 10 year mark where I finally just scrapped them off completely.. :)
The side and rear decals still look great, so that's good enough for me.. :)
I don't put anything on the roof. Just wash it once or twice a year with the automotive soap I use for the truck when it gets really dirty..
I've got an ADCO cover for it, but only put it on when it's stored for the winter.. I tried doing it between trips during the summer, but even once a month as a PITA.. So, I just leave it uncovered during the time I'm using it..
Mine has flaps for the door, so even when it's covered in the winter, I can still get in and we use it for an extra room too. Just use electric heater and they can't use the toilet..
Good luck!
Mitch