Downtown SD? - whoa- lived north of SD for 30+ years- parking downtown is impossible...food for thought:
Marinas - some have big parking lots to accommodate trucks and boat trailers - contact the marina's manager he might have room?
General Aviation Airport ( Clairemont Mesa, Carlsbad, Ocean side) all have airports - might be able to park next to a hanger
Kearny Mesa has a large number of manufacturing sites - talk to a rental agent..maybe they'll let you park in a parking lot near a large building for rent.
There is a large Harley Davidson dealer near the 5 fwy - MC dealers get desperate when the economy gets tough...maybe he'll let you park "out back" for a fee...?
Good luck with your quest....hth
Experience is a tough teacher....as you get the test first and the lesson later