Very uncommon. I know this is an older thread but my class C 4wd conversion was done by Advance 4wd Solutions of Utah and has been flawless. The entire conversion was just over 16 K but that included lift, lockers and on board air which of course have rarely been needed. Just another option for those serious about this if they are still in business.
I would absolutely concur with units like the Tiger being really optimal. I love mine and will drive until she dies but a smaller footprint and girth would be nice but oh how I like my space (32 footer).