One of the main problems with the portable units is the fact that they are portable. That is others can easily take them. Also, each time you move you have to set them up, and take them down. No big deal, of course, but for me, when traveling, I move every day or two, so it gets old. Another thing to consider, if you are traveling a lot, like I do, is that the fixed mount (roof systems) charge as you travel to supplement your TV charge, and when you stop for lunch, rest areas etc, the roof mounts are still working.
I did portables for a time, then finally made a fixed installation on my Argosy 20'. I like that a lot better.