TECMike is right. Whereas many of the other posters apparently have no experience with towing a Casita or similar 'egg' trailer.
I have had an 8' wide Rockwood and a 7' wide Burro (molded fiberglass 'egg' similar to Casita). I now have a 7' wide KZ. The Burro towed noticeably easier than either of the others. Wind resistance is a huge factor in towing. Much more so than adding a thousand pounds or so of weight. I got 14 mpg with the Burro, 12 with the KZ, and 10 with the Rockwood. Many Casita and Scamp owners get 15-16 mpg (the Casita is more like 6'8" wide, whereas my old Burro was 7'2").
Not only is the Casita narrower, it is also lower in height and rounded on the edges and corners. Much less frontal area. The rounded shape all around is very good at cutting through the wind vs. a more boxy trailer. Your drive train will thank you for getting the Casita.... that is, unless you have a big diesel, I guess.
