I use a layered approach. It's simple but it also keeps the tower level so as we pull the boat out it clears the garage door assembly. The layers are motorcover to tower top: towel> Firm plastic storage tote lid> 3 stacked 5 gallon buckets. I can access both side rear holds to let them dry out or unload stuff easily.
When I need to get into the motor I brace the tower similarly on both sides so I can wiggle into that hold without getting tangled in the tower.