Hey there! Yes, I had a similar issue. Loading the boat on the trailer at night was tough at dark and backing into the garage at times was difficult.
I installed LEDs on my trailer that turn on when I put the truck in reverse. The LEDs on the trailer help a little with backing but not enough to light the garage.
If you have electricity in the storage unit, I would try to wire a few lights in the stall that would turn on when needed.
Bluewaterled.com will have what you need.
Capt. Craig Copeland
2013 Nautic Star 2110 Shallow Bay Boat
Nautic Star Boats Pro Staff (nauticstarboats.com)
Redneck Fish'n Jigs Pro Staff (redneckfishn.com)