I went to a local shop that install CB on motorhome. They say the no ground antenna will work well to communicate between motorhome and this is what they install now. The antenna have to be mounted with a lenght over the top of the MH. They will test it and find the proper spot to be mounted.
They did install grounded antenna before but he said it was a hit and miss to find a good ground. Since the antenna have to be mounted above the MH, ground is hard to find and not sure if it connects properly with the rest of the MH He also said sometimes they had trouble with ground noise or spoty reception with a grounded antena on a fiberglass MH, hence, they do not install grounded antenna anymore on MH.