My to DD's are 9 and 17, so they hate sharing a bed. When we stayed at CSR we packed a twin blowup mattress, and it worked great.
At night we put it between the two beds and in the morning we just proped it up against the wall so the maids could clean.
The only fighting we had to put up with was who would get to sleep on the blow up since they both wanted to.
Denise