Well, if you're looking for size to the nearest half-inch... I'm afraid its not useful information. Travel trailers are not precision instruments and there is some variation from trailer-to-trailer.
As far as length, the frame on my 171 is just over 18' long (maybe 18' 4") and the spare tire sticks out about 20" - although there is a little bit of play in the spare tire holder, so it may actually bounce out to 22" when I go over a speedbump. Width-wise, from wheel arch to wheel arch its a hair under 8' wide. Height-wise, its about 9' 6", but I wouldn't go under a bridge that was less than 10' high (and even then, I'd be inching my way through).
If I was locating my r-pod in a garage, I'd want the entranceway to be 9' wide by 10' high, and the garage to be at least 20' long (preferably 24') - even still, that'd be pushing my backing-in abilities.
On the other hand, if I'm booking a campsite, an 18' site is fine. There may be some a foot of overhang at the back over the grass, but who cares?