I removed my toilet and use a Thetford 550 toilet. I just used some aluminum tape and covered the hole over from the inside and outside. I too thought about applied foam to the hole, but have not gotten around to do that yet. My TM had two separate drain connections, so for me all I ended up doing was remove the bolts from the flange inside and then cut off just below the floor bottom. Was not easy to cut it off, cause I had a very bad angle and access.
Now some folks have installed a cassette toilet that you can remove the tank to dump it from the outside. That would be my next big mod. Not sure if you'll have access to this section, if not I would suggest you become a member.
http://www.trailmanorowners.com/foru...assette+toilet