Welcome to the site RJNH.
As a NH resident, you know how salt affects vehicle undercarriages and body's.
Hopefully this shuttle you are focusing on is from other parts of the country and not from here in the rust belt!
I looked at literally dozens of potential candidates around here that were too far gone, (in my mind), to invest in. Some were only 5 or 6 years old and had rust encroachment that would have taken way more than I wanted to spend to fix.
Forget about anything 10 years and older that has lived its life up here, unless you are prepared to spend $$ and time fixing rust instead of converting a bus to a camper.
After several months of daily searching I found one in interior North Carolina that was clean and rust free. The auction site govdeals.com was where I found it. There are other sites that would also work in locating a safe base to start from.
Shuttle busses make good campers however their overall structure is not as robust as a metal bodied school bus. Think heavy snow loads on the roof in winter.
Then we focus on engines that power the bus. Please do your due diligence in researching the various power plants that Ford has used over the years in their cutaway vans.
There are good ones and some questionable diesel offerings that should be avoided unless you have deep pockets to remediate the shortcomings.
Member Cheese_Wagon on here has some interesting reads on getting into the hobby/lifestyle that might enlighten you on how to pick a good base platform to start from. Search him out, it will be worth your time in doing so.
Good luck in your selection of a vehicle and dreams of converting same.
Post pics if you go ahead with anything...