How do I install horizontal propane tanks in my Lance 1161?

Since the permanent type tanks are 350.00 how about just a rear box on a hitch mount , put in a low pressure disconnect like the ones I`ve had for barbeques on campers , leave the stock propane bottles in place and carry a couple cheap 20lb vertical bottles in the box plumed with a regulator and cross over
Back up to the re-fill station and have them fill the 20`s in the box