Nobody joins and they make it mandatory, isn’t that the usual MO?
They will do it at inspection time. They will calculate your mileage for the year, divide by 12, look at a table and they will add it to your registration fee. Pretty simple really.
To start the program off, they will take mileage since purchase, prorate it to your inspection date and bill you for it. If you don’t pay, they will take it from your taxes.