Had no idea, so this was a good time to measure it.
We're at 22" to the frame and about the same to the skirting. But we've got that stupid Cougar sliding rear tray, so the bumper is only about 18". Which does help to protect the rear jacks I guess. Sewer is in front of the axles, and tucked up pretty tight, so not really likely to hit anything. That last point was something I paid attention to when shopping. I have see too many where the sewer outlet was too far back and too low hung for me to accept.
We've got about 7" of truck bed clearance.
We hit the dirt roads a lot, but stay away from anything really rough. Not so much due to clearance, but more because I don't want to shake the coach to pieces. Never have seen any clearance close calls. Being less than 29' has to be a big plus.