This forum should have some sound answers as far as what you need to handle a 5'ver.
http://www.rvforum.net/SMF_forum/index.php
I have never read anything about a 5th wheel voiding the warranty, but the tongue weights are about 1200 to 1400 lbls and GVWR at about 10,000 lbs on some Palomino models. Not sure if the advantages of a 5th wheel hitch would compensate for that payload on the bed/frame or the real weight you might end up with, but the guys on this rv forum will hopefully steer you right.
I have a weight dist hitch, and tow gears. My tongue weight is 328, dry weight is 4200, gvwr 5800 and after 2 long trips with it, I'm certain I wouldn't want anything more on it, powerwise and handling, although the 5th wheel would handle better.
Good Luck !!!!!!!!
Cheif