May not be what you want, but the best security is out of sight. Add quick release clamps and remove them from the boat when you get home. If you're worried about them being stolen, then that's the only sure way to prevent it.
Boats on trailers tend to be very insecure. In my area, it is unheard of to have alarms in boats, so theoretically all you need to do it cut the tarp and take whatever is loose.
Of course in Canada stuff like this doesn't happen