One thing that seems apparent is that the TM website specifications are pretty accurate. You can find them here for all models:
http://www.trailmanor.com/WebDocs/Sh...ifications.htm
Dont' forget to add the A/C height and also add 2" for a lift kit if the unit has one (apparently all 2007s have one as standard). If your driveway slopes towards the garage door, then the TM will enter the garage at an angle and because of that you might need more height at the door.
It seems that swing hitches can be installed after market if the TM doesn't have one when you buy it - this may be cheaper than adding another two feet to your garage expansion plans. There are various backup sensors which will prevent collisions with a part of the garage. For the length, I think I would probably want to have at least an extra 1ft to play with and I would use one of those devices, e.g:
http://www.reversebackupsensor.com/b...FTaVFQodXxjU5g
-Paul