If you're in the market for a trailer, you may want to have a look at Airstream, especially if you like to stay connected during a cross-country trip. Airstream has extended their partnership with AT&T to bring LTE across all of their trailers.
It's not just the 2019 Airstream Classic that comes equipped with LTE. If you have Basecamp or Globetrotter, you now have the option to get LTE service from AT&T, and all you have to do is choose what you want to pay for.
Unfortunately, there is something else to consider: pricing. The roof-mounted Airstream Connected hardware, which is necessary, will set you back $999, and on top of that, you will still need a data plan to go with it. If you're not interested in paying the $999 needed for the hardware, you could always look to getting a portable hotspot. The hotspot may very well be more useful beyond the trailer.