I ripped a jack off my 5th and bent the spare tire off last year on a rolling/bumpy back road. I already knew it was going to be close and had a buddy standing by "spotting" (still not sure why he didn't speak up :))
My 5th is pretty low slung so it wasn't too much of a surprise. I'd go measure but my pad is sloped so the trailer isn't sitting even close to level. I was surprised how small of a rolling hill it took for the back end to hit. There's just a lot of trailer behind the wheels (35' fifth wheel). The jacks and spare hanging down even further is just total stupidity by the manufacturer. I've since modified my jacks to come off with removal of a couple screws and I can always take off the spare. Unfortunately, 5th wheels just aren't the best for backwoods camping on uneven roads. Between bed rail clearance and back end clearance it can be tough.