What is the ground like in the storage yard? Could you get some of those long screws from Home Depot to tie down the trailer? They don't work too well up here (too sandy) but might work in your area.
I've yet to see the "right" ones at home depot - they have the pig tail type that will worm it's way out
These are the kind we use here in clwt that work well (not sure about in a 186 mph)