I always sprayed mine off in the driveway with my old boat. I haven't cleaned the Lavey's cover yet, but I plan to soon.
My plan is to bring it to the spray and wash near my marina in Needles, after I've launched the boat. I'll spray it off with soap from the high pressure washer, then bring it back and strap it to the trailer to dry in the river heat.
IF the ground is deemed too dirty at the spray and wash, I'll have to think of something else though.
I'll report back how that all goes.....
RTJas