I have the WeBoost Drive 4G-M installed in my B along with an outside antenna. To be truthful I am not sure it improves cellular all that much. It is installed up under my dash board behind the glove box. Advanced RV installed an on-off switch for me on a recent visit but I have not taken the time yet to see if it makes any difference by testing both ways.
https://store.weboost.com/products/drive-4gm
Maybe it does work. I've noticed in campgrounds and such I, more than not, always had a good signal just about everywhere. Is that from the WeBoost or just better coverage year after year steadily improving? Maybe a bit of both.