There is a shopping plaza behind the hotel that may be an option
The road behind is residential. Unclear if you are parking and RV or commercial vehicle. Across the street there is a good size strip mall. I would call local police ask if you can park across the street for a night (or however long you are staying) without being towed or ticket.
The parking lot itself is small, as this is an older hotel but there may be parking out in back of the hotel.
Get an answer from Island Sun Inn staff and past guests.