So affordable, usable everywhere, Verizon, and stream a movie. Better chances of finding an honest politician.
I would not be the least bit surprised if the Mobely deal had a lot of fine print to it, even more so if you were not ditching your verizon phones and going to at&t (or not getting a direct tv subscription).
If you want to stream a few movies with a cellular plan you need an unlimited plan and need to live in a city that gets good bandwidth. Netflix 1080p movie is 1gb pr hour so 2gb a typical movie. That means you need 3-5mbps constant speed which can be difficult to obtain outside of large metropolitan areas.
If you stay in a single RV park for the bulk of your time then my advice would be to get service from a local provider. DSL will usually be cheaper, ultimately it comes down to what service your park has available of course. Many android phones have wireless tethering so if you have android phones then that would be a better option to use while traveling from your summer to winter home.
If you do a lot of hopping then there is really no good option. You are at the liberty of what the cellular carriers charge. Currently there is no good inexpensive plans, possibly something will come up around Christmas time. If you want reliability more than 100 miles outside of major metropolitan areas your choices are pretty much Verizon and Verizon.