Re: Public storage?
You simply have to know about your particular lot. I leave my trailer in an open fenced lot ($40/month) and it's fine but even the owner agrees that if I put my boat in there it would be stripped overnight.
If you store it, check it over carefully before pulling out; one guy here found all but one of his outdrive bolts undone by a thief who didn't complete the job.
A cover helps keep things out of sight. That makes a big difference, as well as anything that will slow him down. IMO the opportunist thief (grab what's easy and tempting) is the one easiest, and most effective, to guard against.
The decision after that on how to secure is purely personal and particular to your circumstances--like asking, "How should I lock up my house?"
Consider the types of thieves you may encounter--the pros who would take a whole boat or OB cannot be stopped. The opportunist won't tow off a boat with a padlock on the hitch, nor will he look under a cover. A thief looknig for stuff to sell may go for electronics but not boating equipment such as a tube or anchor; your fellow boater will take ("borrow") a fender, bow line or paddle. And then there's the gas syphoner. A boat in the water is subject to a joy rider more than a steal-to-sell thief.
So for example, a boat i leave at a yacht club is subject at most to "borrowing," which is aggravating, but not thievery of valuables. I could leave a GPS sitting out but not a bowline. Cheap and easy enough to solve.
If you try to lock up against all types of thieves you become a victim of a crime that has not been committed yet, with the expense and inconvenience.