Build 2 chocks from 2x salt treated wood. Use plenty of screws.
Screw a piece of salt treated plywood to the bottom each chock using plenty of screws. Make the plywood the width of the chock side to side, but longer than the chock from front to back leaving it long enough as needed to extend under one tire on each side.
Back the trailer close to the garage door and place the chocks in front of the front trailer tires and roll the trailer onto the plywood making contact with the chocks. The weight of the trailer will keep the chocks from slipping and the trailer from rolling down hill.