attuco,
I think you misread something. In Michigan, the max $300 ONE TIME fee for a large heavy towable over 10,000 lbs dry is forever. No yearly fees ever. $200 ONE TIME fee for 2500 lbs to 10,000 lbs dry weight. $75 ONE TIME fee for up to 2500 lbs.
Owning for 10 years and paying $300 for the one time non-expiring plate = $30/year. Paying $200 one time = $20/yr. Paying $75 one time is $7.50/year.
Boat trailers etc one time fees are for the bare trailer itself by manufacturer's title weight as shipped from the factory. Cargo carried on any trailer has nothing to do with trailer registration weight.
Some states base their registration fees on total weight on the vehicle's and/or the trailer's tires to determine their registration fee amounts and what the unit is allowed to weigh legally. Big fines if you exceed the registration limits.