Love my Chromecast! Don't understand your problem. I use my Galaxy Nexus as a hotspot and send Netflix (I have unlimited data) and screen pictures to my TV.
I also have Wilson Sleek and usually keep the phone in its cradle. I put a Wilson Trucker antenna attached to my crank up TV antenna and ALWAYS get good enough 4G signal for pause free movies etc.
I would never rely on WiFi from the campground and its not fare to other campers to choke up the campgrounds net with movies anyway.
I'm probably going to get a second Chromecast for our smaller TV in the bedroom.
Ron W.