If you want to build a dam yourself there is a material I know that works very well. It is tough and flexible and designed to last long. Look for hay baler belting or repair belting. To attach it to anything for this purpose you would use a small metal bolt with a wide waster and crank the bolt down tight. You could probably put it on the bumper since you can get it up to 10 (maybe 12) inches wide. It is made of a very tough rubber with 1+ nylon ply. I'm building a rudder system for my kayak out of it so after much exploring different materials I picked it as being the cheapest/most effective/longest lasting alternative. You may want to look into it for repairing your RV.
Here is a link. I found it at Tractor Supply Co just because I used to work there so I know what they have. Any co-op or ranch supply store should have it.
Replacement Baler Belting, 10 in. Wide-2 Ply-210# Nylon/ft. - 1420017 | Tractor Supply Company
I suspect that if you put it on the bumper in one piece will angle it towards the truck and make it more rigid so going over stuff forwards shouldn't be too bad. Backing over obstructions, however, will. If you do strips hanging from the bumper there shouldn't be an issue but it will probably not be as effective.
As for the rims, see if those cheapo clip on rims from walmart will work. Most of them are designed to look like dinner plate wheel covers and they will at least have openings for air circulation.