There are times when you want to use your cell phone, but you're a bit too far from a cell tower to make things work. You can get a cellular amplifier to help with the situation. Basically it's a roof mounted antenna, an amplifier and an interior antenna. The outside antenna is up high, away from the van and sensitive. The amplifier takes this and boosts the signal it can find. The interior antenna is small and meant to be used within a couple of feet. This is so the inside and outside antenna don't "see" each other.
I mounted the roof antenna on the roof rack with a swivel joint. I figure I put it up only when I want it so that it doesn't get snagged on stuff.
WB provided a nice roof access port on the 2021 so you can easily get the antenna cable into the dinette cabinet. I chose to run my cable behind the cabinet interior as well as wire in the power supply.
Since the power supply is permanently wired in, I needed an ON/OFF switch. I used one of the laser engraving companies to get a custom lighted switch. I milled up a bracket out of aluminum and stuck it on with some VHB. It's located just above the amplifier on the outside of the cabinet. Works for me.