You know I never thought of doing this, but its a great idea. I have used a storage tent when I have tent camped, but never thought of it while we were using the camper. I think its a great idea. I'm not sure what you would use internal to hang towels on, but I'm sure you could do it. I'm thinking my tent has a few clips to hang a room curtain. I bet you could rig up something along those to spots to hang towells on. My biggest concern would be how do you stake the tent. Depending on the style of site, you may not be able to drive a stake down in the ground on all four corners of the tent. I know the newly upgraded sites have a full cement pad.
Last time we went I bought a clothesline for the bumper of the camper. We hung our bathing suits and towels there. It dried things quickly and I had a spare set of towels in case of a rain.