I've been using a Protect-a-tow for several years over my dolly. The front attaches to the rear bumper of the MH and the rear uses two bungee cords attached to large S hooks mounted on each side of the dolly. See below:

It does not fully reach the toad but is seems to keep most of the larger stones off the toad and really keeps the MH rear & camera clean. I think Protect-a-tow sells a longer model that might do an even better job but I’ve not needed to replace mine yet. I have a Demco KarKaddy and there were two holes on the wheel plates that the S hooks fit into. I don't know what king of dolly you have so I can't suggest how you would mount yours.
Dave