I would suggest you give Mayflower a call.
a) launch for free on the public slip next to Mayflower
b) pay an overnight fee and moor inside the marinas security zone. CCTV everywhere, 12 hour boat checks, 24/7 security etc.
c) this fee SHOULD (ask them nicely) allow you to park your boat/trailer and/or car inside the security zone of the marina.............and they are nice people.
d) you can then recover again via the public slip.
If you run into any problem, the marina staff will help you, there is a chandlers on-site, there is a marine engineering business on-site, there is a restaurant/coffe bar/bar on-site.......etc