How to run Coax for booster antenna out of Fold Up Camper

Heading up to Camper on Monday and will measure for Coax.. All I found on Amazon was 30 ft coax and I would have to get an adapter for coax to plug into the SMA on the booster. I like your idea. I'm guessing the Fold up camper is around 11 ft
in height so the mast will be 15/16 ft up and then run the cable in through under the rear canvas and under the mattress, I may need only 17 - 20 ft of coax.