Add me to the "no you do not need bottom paint" crowd. When I bought my 26S, the previous owner kept it on the trailer, just as you plan to do. No bottom paint. This is ideal, as even the best anti-fouling paints will not be as "slick" as a good, blister-free gel coat.
Since I keep my boat in a slip (fresh water), I decided to apply an epoxy barrier coat to avoid blistering, and an anti-fouling coat to discourage algae growth.
If you do have the boat in the water long enough for algae to start growing (2 weeks in the summer in fresh water, less in salt water), be sure to remove it as soon as possible after you haul it out. The longer it stays, the harder it is to deal with later. A 6" plastic scraper and a wet towel will be all you need.
Should you decide to keep your boat in a slip, you will want to consider applying an epoxy barrier coat, then an antifouling coat, ablative or otherwise.