Welcome to the forum.
If you're not getting on the roof because of a fear of heights, that's one thing.
If you're not getting on the roof because you don't think it will hold you, that's different.
The roof will safely support you.
How will you clean the area and apply the Dicor? If you can do that, you can apply the coating from the ladder.
Personally, I would (and do) get on the roof to apply the coating.
I do use scaffold to work on the edges but, get on top to do the rest.
Can you borrow or rent scaffold? It's a lot safer than a ladder.
Can you have your son help? He should learn the maintenance procedures if he's going to use the RV. Or, will you do all the maintenance?
