If this is a "real" park model (11-12 foot wide, not the old style 8 1/2 ft with tipouts and EPDM roof) then I assume it's shingled like a house? Easy enough to put a metal roof on it.
Otherwise treat it like you're looking at a house, the park model I'm assuming is built with 2 x 4's 16" on-center, likely an 8" frame. Look at the floors, any leaks, warping, etc. Since you're in Michigan, assume frost will heave over the winter, keep an eye out for cracks in the walls/ceilings. Check the siding too. On second thought, have a professional inspect it for you.
Nice that you don't have to pay property tax. On ours, property taxes for the year on the entire lot that we own (Minnesota room plus park model) is only about $300. I can see it going up a bit in the future though.