Hi David!
Much depends on your local fouling conditions, ask around local marinas.
Cruising in the teens is enough to use ablative paint...most trailerable boats do since some hard (but no ablatives) lose effectiveness when hauled for more than x days and have to be re-done prior to launch (expensive). Hard paint is smoother and faster for sailboat racing or if you're on the C-Dory Pro Racing Team.
We have 92 degree saltwater and without prolonged use we can get slime and hard growth in a few weeks; for $70 a diver takes care of it. Our beach destinations are only 1/2 to 3 miles from our marina, so we are outliers there.
If you choose an ablative, use a water-based one so you can 'touch up' on the trailer safely and legally and put everything in the regular trash...Pettit Hydrocoat or Micron.
What's on there now? You can paint soft over hard but not hard over soft or anything over vinyl. You'll want a 2-part epoxy barrier coat of contrasting color if not already there so your dock-mates can point out when it's time to re-paint. For most it's a pro job and soda blasting involved.
There is a pretty good article on West Marine Advisor on top 10 bottom paint issues.
Owners dicker about this, there is no universally accepted agreement like there is about twins are always better than singles because they look so cool. (just kidding!)
Happy Researching,
John