hi I donít have a Casita
, but I did install one in my Lil Snoozy
which is about 17 1/2 foot. I would recommend that you go for the larger unit which is about 3000 BTU more heat output. They also have a unit that you can mount outside of the coach and run the heat ducts inside.
these are very nice furnaces and very quiet. Best of luck with your project. Dave and Paula