I'll throw another thought in here too that I don't think has been mentioned. Some of this ease of towing regarding width has to do with "where" you tow. If you stick to the interstates, and generally operate on wide well built highways with paved shoulders, then a wider trailer is "easy". But if you frequent twisty, narrow county roads that have no shoulder, then you will have to pay more attention to the width of the trailer while in tow.
I would not say it's more difficult to deal with the wider trailer, it's just that you have to pay closer attention to avoid dropping right side wheels off the edge, or to avoid getting the left side too close to the centerline.
As for the difference in fuel economy, I tow either my tall boxy camper, or a shorter, more rounded edge two horse trailer with my Nissan truck. The lower more rounded horse trailer allows me on average about 2 mpg more than the camper. They coincidentally weigh about the same. I would expect if I pulled a Casita/Escape/Scamp type trailer I would get another mile or two even better, but that is just a guess.
More important to me is the "livability" of the camper once I am parked, because when I am out in the camper, it's usually for several months at a time. So wider, taller, and a slideout room are mandatory for me.
