In my several experiences with the Thetford, I've had two problems:
1. For that rear bolt that Bob describes (see the PDF, too), you need a really long extension on your socket. A little bit of chewing gun inside the socket itself helps, too.
2. Removing the toilet is much easier than reinstalling it. The main problem is trying to get especially the rear coming up from the flange to align with the hole in the bottom of the back of the toilet. (My big hands are unhelpful in this regard.) It did help to go to the hardware store and purchase extra long toilet bolts, which gave a little extra room for my hands to align the bolts.