Anti-Fouling for Trailerable
There's basically two kinds of anti-fouling paint. Ablative and bio-cides. Each has its advantages. Ablative is great is you're not a speed freak (it's not the smoothest of paints). Basically, it (and sloughing paint) wear off as the boat moves through the water taking the growth with it. And there's the rub...pardon the pun. Sitting at the dock, ablative paint allows some growth. It takes motion through the water for ablative paint to do it's job. Normally, if you're going to take the boat in and out on a semi-frequent basis, or sail a lot, ablative paint works fine (that's what I use). Plus, ablative paint is pretty cheap by comparison and easy to apply.
Biocide, on the other hand has the advantage of being available in a smooth, high-gloss (looks better and adds a little to the speed). It works by basically poisoning whatever starts to grow on your boat. So, it works whether you're moving or not. However, it isn't something you slap on with a roller and, I think, is more expensive (obviously from a labor point of view).
So, if you let the boat sit for months at a time, the biocide is probably your better bet (if you want to spend the money). You can Google this question and find all sorts of info. But, I hope this helps.