Might be a warmth advantage to the rat fur??? I can tell you, going into that Casita bathroom on a cold night, reminds me a lot of the cold outhouse we had as a kid. We try to remember to keep the door open at night.
Casita cost the same as Scamp when add the Scamp add ons.
...but Casita does not make a fifth wheel, which is the Scamp model the OP is considering.
A used Escape 5.0 single axle is close to a Scamp 19 in size and has a full fiberglass bath enclosure. No longer made and hard to find used. Standard longways bed is an advantage.
Scampy
Linear Mode
