I think I would fill more than a 2x2x4 unit, considering that the back of my van is full right now and doesn't actually have the whole kit yet. But you're right that I should check the $1 move-in specials.

Another idea that Lisa suggested, which preserves the 24-hour access and is possibly more secure than storage in the van, is to rent a small U-Haul trailer, use it to hold the gear during the con, store the gear post-con in the lockers there for later retrieval, then turn in the trailer at the U-Haul outlet located right there on Virginia St. near the Peppermill.