Paint for a utility trailer needs to be tough, abrasion-proof and weather-resistant. Assuming your utility trailer is going to spend some time exposed to the elements, the best paint should be formulated for exterior use. Further narrow down your options by choosing between water-based and oil-based paint. Consider floor and deck enamel for painting a wooden utility trailer.
Preparation is Key
The secret to every successful paint job is in proper preparation of the surface. Remove any hardware, such as tie-down hooks and latches, for a neater job. If the wood was previously painted, scrape and sand away all loose paint and surface dirt. Bare wood requires no surface preparation as long as it's clean and dry.
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Choose between latex (water-based) and alkyd (oil-based) paint. Latex is easier to work with because it dries faster and requires only water for cleanup. Premium quality latex paint is durable and easy to touch-up. Alkyd paint takes longer to dry, and you'll need mineral spirits for cleaning up. However, a good alkyd paint is more abrasion-resistant to even the best latex. In both cases, the higher the gloss, the harder the finish coating.
Unless your utility trailer will only be used indoors, choose exterior paint. Interior paint will not hold up well for long at all if exposed to sunlight or rain.
Consider exterior floor and deck enamel. Because it's designed to be walked and even driven on, it's harder than paint formulated for walls and siding. Floor enamel is typically available in sheens from satin to high gloss and in most colors. Another reason why floor enamel might be the best paint for your wooden utility trailer: it is self-priming, meaning you do not need to apply a separate coat of primer to bare wood.
If the trailer flooring is plywood, consider not painting it at all. In normal architectural flooring applications, plywood is used for sub-flooring and not as the final floor. It does not take paint well, even if you use a premium deck paint. An excellent alternative for plywood trailer floors is simply to use a deck stain instead of paint.
If you opt for painting the trailer floor, add a skid-resistant additive (see Resources) to the paint. Glossy painted flooring can be quite slick, especially when wet—adding some grit to the paint will make it much safer.