Welcome to the insane asylum.
In choosing the right bus, the task for which it will be used, will best determine the 'right build'.
How do you plan to use it? Haul an off-road machine, tour with a band, raise six kids w/cats&dogs..., weekend rock climbing, party bus, mobile workshop/office?
As far as durability, eh, they generally retire these buses when the expense to maintain them has exceeded the counties' budgets.
If your dream is only to perform the conversion, not use it. Then disregard what he just wrote. I told him not to write all that.
Did I mention insanity?