Although I've never owned a fifth wheel, I've always flipped the axles on my travel trailers. I tend to go into some strange places, and I do not want to bottom out the trailer anbd wipe out either my water or sewer piping. I usually gain 3.5 - 4.5".
Flipping the axle
is no big deal. You can do it yourself, but mark the axle
positions so that they are in the same spot as before. THis is important for trailer tracking. Also, use new U-bolts. This is not the time to save a few pennies and lose a u-bolt that has failed.
If you are not handy, take it inot a truck spring place. T^hey're used to doing this sort of thing. Also ask for an alignment check.