KampingKris,
First off, the ladder on the back of about 99.9% of these coaches will tolerate the "over weight" (if I may for sake of conversation) for short periods of time. They (the builders of the coaches) know that not every one that purchases a coach is not tiny. What they don't want is someone "hanging" a ton of stuff, i.e. Spare tire and wheel, tool box, and a few million other things that people WILL DO unless there is some sort of "limit" placed in/on it.
I too am 240 and regularly climb on ours to get up there and do maintenance. Now, ours is fiberglass too and, I'm one of those that really keeps the roof nice. Why, because I like to and, I get to keep an eye on all the seals, caulking, vent caps, vent covers etc. that can get damaged or, start to deteriorate and, because they're up and out of sight, many don't know it 'till it's too late.
I just finished my annual machine buffing and coat of wax on it. Yep, it does get slippery, especially when wet. I did it last August and it was a pain due to the fact that, the roof had never seen any maintenance prior to our purchase of the rig. But, this time, it was a breeze. Between the machine buffing and a hand coat of wax, about 8 hours. Now, it's good for a year, and I keep it under a drive-under cover. It only sees the sun when we're using it.
As for washing it, I do it two different ways. One, the cover is too low for me to stand up and wash it so, I stand on a nice, sturdy ladder and use a long handled brush with regular soap an water. Then rinse with the hose. The other way, when we get back from a trip, prior to parking it in it's "garage" (pole and tarp cover), I climb up there and do a quick hose down, wash, rinse and it's done.
Not many folks maintenance their roofs on these expensive rolling gymnasiums and it's nice that you are concerned about getting it done. So, in your dilemma, your husband, may be a bit over the "labeled" weight limit of the ladder, I doubt that ladder will "tear" off the back of the coach for the brief time he's on it to climb up and down for some "once a season" type of maintenance.
But, if you're not comfortable with that, then maybe you could check around for some RV detailers in your area and see what they might charge. It's usually by the foot but, not always. When I was growing up, there was always kids around wanting to earn money and many of them washed your car/truck etc. But, they're all playing NINTENDO NOW, so that idea's out. Good luck.
Scott
Scott and Karla SDFD RETIRED2004 Itasca Horizon, 36GD Slate Blue 330 CAT
2011 GMC Sierra 1500 Ext Cab 4x4 Toad
2008 Caliente Red LVL II GL 1800 Goldwing KI60ND