We live in MI. All our trailers both TT and Fiver were permanent plates - buy one time. A MH is different and your plates are annual (tabs) fees based on your purchase price. Our plates (tabs) would be over $1200 per year and we don't have a high end coach.
We get around that by paying for two months at a time ( every 60 days you can get a temp). It's only 230 but I can get by with 3 fees ( 6 months). Saves a lot of cash parked all winter. So if you're gonna let it sit you might consider that option.
You will pay Michigan tax no matter where you buy it. MI. Secretary of State will get it from you when you get your plates.