Add a Room in chilly climate

We spend January through March in northern Florida.  Temps on some days only make it into the low 60's.  We have a small trailer and are considering an "add a room".  But we would like that room to be comfortable even on those chilly days.  Does anyone have experience with a high quality add a room?  Ideally we'd like one that uses inflatable tubes rather than poles, but the only source we've found is an Australian company called XTend.  But we can use one with poles.  Any thoughts on safely adding some heat for those chilly days?  We realize that some sources of heat add moisture--we don't want water dripping on us!  Thanks for your feedback.