Our Montana was treated with ResistAll when we purchased it. We are now going into our 4th year of ownership and the camper has never had any kind of wax on it, as it is still shinny as new (when it's clean).
With that said, first, mine has never been waxed, and the roof (Alpha system) has been cleaned and treated only once (a few weeks ago).
But, mine has had many baths.
Here's what I used, and have always used on all my previous trailers as well as the one we currently have.
1) awning: Mr. Clean Magic Eraser. Not easy, but the results are great! Simply make the sponge wet (not dripping) and wipe the awning. Follow with a dry towel. If all the crud does not removed, wipe again (do not scrub, just wipe), and dry with a clean towel again. Do it in small sections and it's manageable. After it's clean, or if you do the Mr. Clean Magic Eraser when the awning is new, the black mold growth is greatly reduced. Minor touch up's through the Summer to remove dead bugs that get squashed in the awing, and you'll never have an unsightly awning. There's something in the chemicals of the Mr. Clean that KEEP it clean.
2) Road tar that splashes on the side, front, end: WD40. WD40 will simply melt road tar off. Wipe with a paper towel and it's all gone. It works fantastic on your car and truck too. It does not hurt or damage the paint, chrome, aluminum, or fiberglass. It's also good for removing splattered bug juice. Just let it sit for a few seconds before wiping the bugs off. But for road tar ... this absolutely cannot be beat.
3) Sides of the camper. Others will differ here in their opinions as everyone thinks they've got the best solution since the Beverly Hillbillies discovered lye soap! But for my vehicles and the sides of all of my trailers, for over 25 years, aluminum, fiberglass, metal, paint, .... it's always been a mild solution of Dawn Dishwashing Liquid.
Dawn Dishwashing Liquid is made to dissolve cooking grease. But it also dissolves petroleum based oil and grease also. (Think of those commercials on television where they are washing the oil slicked baby ducks)... It's true!
The reason so many folks do not like to use Dishwashing Liquid is because it does remove car wax also. It cleans fantastic... maybe too good. Rinse real good and hand towel dry so there is no streaking. Or wash with water that's that's been filtered through a water softener. I plumbed an outside faucet connected to the lines from our water softener, as we live in the country and have heavy iron in our water.
4) Tanks. You did not ask about your holding tanks, but you cannot over look them either. In time, they WILL smell. The easiest way to keep your tanks from smelling is to use lots of water.
Grey tanks or black tanks, drain all the contents. Flush with extra water if you have a water source and a sewage source. After draining and flushing, put about 5 gallons of water in each tank, add about a half cup of Dawn Dishwashing liquid (or Tide, or any kind of laundry soap ... NOT THE PODS) ... and take the camper for a drive. The sloshing of the soap water will clean the insides of your tanks, keep "stuff" from clinging to the side walls and top of the tanks, and make the contents easier to drain out. Once you arrive at your next destination, drain the tanks, or just leave the Dawn and the 5 gallons and drain when the tanks are full again. If you do this EVERY time you break camp, or leave home to go to camp, your tanks will never smell, and will always be clean.
Granted, the black tank will never be hospital clean. But the contents won't build up in the tank either. It will always flush out.
Others have different methods that they swear up and down work just as well, and probably they do. But for me, this has been my method for over 25 years and it still works well.
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually