14 foot doors are common among service and storage faciities catering to RVs, and many are higher still; storage units should state it on their info sheet or website. Most of our rigs are in the vicinity of 12 and a half feet. In a pinch a person can gain some inches by dumping air from the bags - you just darned well better watch for rafters, lighting, and other device once inside if the coach naturally wants to air back up. And any anxiousness to depart better not overwhelm remembering to dump first. I've lowered to clear tree limbs; but you can't turn the steering wheel away from straight ahead in a dumped scenario or you'll damage wheel wells, etc., and you shouldn't negotiate rough spots at any speed. I just creep ahead very carefully regardless.
On our coach, Monaco jumper-wired HWH's control module such that you must hold the dump button down to stay down. HWH configured it to stay wherever you let your finger off the button. Monaco didn't want people neglecting to go back up (or down) and hitting the road at other than Travel height, so releasing the dump button automatically takes me back to 10 inch bag length.
As an aside, it's a pain to keep a finger on the Raise button, which works the same way, when backing at a turning angle over my driveway entrance dip, trying to concentrate on maneuvering into the narrow space along our garage, and then keeping the mirror barely over the top of the adjoining fence for the 30 foot trip back to our pad. Someone yells you are getting close to a garage gutter or something, you let your finger lift off the button for a moment when you try to turn to look, and the mirror slowly descends down on top of the darned fence. I've often sworn I was going to find and disconnect that Monaco jumper wire.
Joel