We've never had any problem with the size restrictions. We travel with a Great Pyrenees that is well over 100 pounds and we have never been turned down at any RV park or charged extra. Since we don't travel with any kind if a schedule, we never make reservations and have never been restricted from any RV park that had a vacant space. I agree that you may run in to a few parks that restrict the number of pets but if your dogs are well behaved, that should not be a problem.
If an RV park is not full, we will usually ask for a space that is away from other campers just to make it easier for us to keep our dog's attention focused to do it's business.
Carry your own supply of bags to pick up after your dogs and you will have no problems.
Try to get your dogs used to being barked at by other small dogs. For some reason a lot of small dogs just like to bark at large dogs. Our Pyr just ignores them and the other dog's owner usually thinks it is cute while his pet goes crazy.