Uh, guys, this is spelled out in the HUD code already...
From 3280.803 (k) (3) (iii)
" (iii) The neutral conductor shall be connected to the system
grounding conductor on the supply side of the main disconnect in
accordance with Articles 250-23, 25, and 53 of NFPA No. 70-1993."
See, in a park, the feeds to each individual home are actually sub-feeds, so the grounded and grounding conductor should be separated. The bonding of the neutral bus has already been done upstream.
This is why these homes come ready to hook up with the two bars separated -- the majority of these homes are set up in parks.
However, in a home set up outside of a park and on private property, and fed by it's own service, then the neutral bus in the main should be bonded for safety reasons, as well as compliance with both the HUD code AND the NEC!!