Take pictures of boat in your spot..........
Do you have a written copy...rental agreement/storage contract etc.---that shows assigned spot (spot number identifying specific spot)?????
IF you do............call tow company and have boat removed. DO NOT MOVE BOAT YOURSELF
Otherwise......park your rig in an out of the way area (along side driveway/in corner of parking lot on sight/not specific storage area)
Leave note on rig why it is parked there with your phone number.
And continue to blowup owners phone with messages/text.....every 10 mins.