Postscript: Despite phone calls to Bigfoot
dealers and posting here and the Bigfoot owners forum, I never did come up with the Thetford china upgrade model that some dealers offer. I have just completed installing a SeaLand Traveler, model 111, aka Lite, low profile. There is about 1" clearance on each side and 1/4" in back. The flush lever had to be trimmed 3/4" to avoid contacting the wall. Tight fit! The flange had to be rotated 45 degrees, which required relocating 8 flange screws. If I had to do it again, I would use the universal mounting flange from Sealand, as relocating the flange was a hassle. The bathroom floor is a sandwich of 3/4" plywood covered by fiberglass on both top and bottom. To avoid drilling (pilot holes for the screws) through the floor and damaging the holding tank, it is important to use a guard on the drill bit or insert something between the floor and tank to act as a shield. I used a small Stanley pry bar. The bar cannot be inserted unless the flange is removed.
We chose the SeaLand traveler Lite because it is similar to the toilet we had in our Casita
. It seems to be a popular upgrade in vintage trailers, such as Airstreams. We bought ours from the CW catalog; the stores don't seem to stock it. The first toilet arrived smashed to bits, but CW sent another right away. Bottom line: this was not an easy DIY project!