Suburban makes units up to 20 gallons that are propane or dual fuel. If there's enough clearance and you can stomach cutting a larger opening in the side of your rig and reframing it, it's not hard to go from 6 to 10 gallon. I've got a 10 gallon on my rig, would like to eventually upgrade it to a 20 as the front foot print on the outside is the same.
Our new fifth wheel is basically being used the same. We travel with our original, far smaller RV since it can make it up the mountain roads, the Bighorn will be the weekend cottage.