Sam,
let me address these separately. For the floor (i.e. inside of the hull), the consideration has to be that there is likely to be standing water at times and many paints that would otherwise be fine will have strong objections to that kind of treatment. On my boat, the damage initially was confined to underneath the wooden floorboards. In some cases the latter had rubbed through to the laminate. My solution at the time was to get a transparent gelcoat paste. EverCoat, I believe, is the brand name. Their transparent ("neutral") gelcoat is formulated to cure in air. I used that to build up the areas the floorboards had been resting on and extended it a bit across other badly worn paint areas (after removing loose paint). Then I covered things up with the floorboards and went back to sailing. Nowadays, I leave the floorboards at home, so a new coat of paint on top of the gelcoat repair wouldn't go amiss, but I've not been able to bring myself to launch into a full repainting project.
For deck and seat surfaces I would not hesitate to use Petit's EasyPoxy paint. I found it easy to apply and it becomes very durable, but you must let it cure for a couple of weeks at least (initially it can be rather soft). I did my transom with it, so it handles some exposure to water, but probably not standing water. There are specially formulated "bilge paints" that should handle the water, you might also look at pool paints.
Now, onto the wood trim and floor boards.
You essentially have three options there:
- Oil: a wood oil is easy to apply and to touch up, but is not glossy and will require frequent maintenance (which can be very quick). Oil will not keep moisture out as well, but would allow the wood to dry out again most easily of these options. Because it penetrates, it's not damaged by scraping or dropping something on it.
- Traditional varnish: varnish would be more durable, but it doesn't seal the wood completely, so it continues to swell and shrink with changes in humidity. As a result, the varnish will eventually crack and you will need to sand and reapply. On a sharp corner like the top of the coamings, it can be scraped off, and may suffer from being walked on (floor boards).
- Epoxy seal, before varnish: if you completely seal the wood (including any openings) with an epoxy product, (such as ClearCoat from SystemThree) you would stop the moisture cycling and provide a very firm ground for the varnish. The varnish is still needed because epoxy doesn't tolerate UV, but it will last much longer and you can use polyurethane ones that can be pretty strong and scratch resistant (I've used Satin WR-LPU from SystemThree, for example). I did my coamings and thwarts (boards connecting the CB trunk to the seats) this way and it's held up for many seasons (with occasional touch up of the PU - it handles a lot of use, but something sharp will scratch it). If the epoxy ever fails, it will take the most work of all three options to get it off and restore.
I've now also done the little wooden shelf that was under the transom deck this way, and am working on doing the floorboards as well.
I'm not sure whether I'm doing the right thing with the floorboards, because the epoxy seal method requires something like perfection in making sure there's no way for water to get past it. I think that's probably impossible to achieve for the floorboards, because of all the fasteners. And floorboards are likely to be awash at some point, so that water would have a good chance to get to any little point that's not perfectly sealed. I'm committed to this approach at this point and will eventually see it through and report here. A the moment, I've stopped using these altogether because I can do without the added weight in racing.
For things like coamings, thwarts, and transom shelf, I can report that it did indeed help to sharply reduce the annual maintenance required. With the catalyst provided, the WR-LPU cures into a very tough surface, well suited for sitting on (like for the thwarts). The sharp top edge of the coamings is a bit of a problem, there are small defects from scrapes and nicks, but I'm usually able to touch them up locally. (I've learned to use a short strip of electrical tape below the tiller: if I lean on it, it can make contact there).
Generally, the three options have an inverse relation between the ease of maintenance and frequency of required maintenance. Oil, you would just wipe on, but may have to do that more than once a season. On the other extreme, Epoxy sealed varnish (PU) is really tough and requires no maintenance other than repairing any damage for years. If / when it needs to be replaced, it will be a massive undertaking. I tried varnishing the floorboards and other trim after sanding them down to bare wood and was dismayed when just a couple of seasons later I was faced with the same task again, that's when I switched to the epoxy seal method.
Hope this doesn't overload you with choices, but there it is.
I store my boat covered and I think humidity cycling rather than UV exposure is the main factor that leads to failed varnish. If you keep your boat uncovered under a Texas sun, you may possibly not be able to replicate my experience.