Hi,
Your
painting marine grade
fiberglass. Interlux perfection is wonderful stuff. It is a 2 part urethane and expensive. Your best price will probably be on Ebay. I'm thinking you will need a gallon for 2 coats. It is self leveling. It is best to have two people when you apply it. One person will roll it on while the second person "tips" with a brush to remove any runs or imperfections. You want a rag and thinner, special thinner for 2 part
paint, to keep the brush clean with no build-up. Prep is everything to a paint-job. Anything that shows with primer will show with finish. Start at the lower rear of the trailer as the spare tire,
lights and
license plate will hide your first attempt.
I have had good results with Interlux Perfection on my sailboat. I have some seats that I built in the cockpit that are open to weather, sat and stepped on. The
paint still looks good after 14-15 years. The deck was painted 7 years ago and is holding up well.
You-tube can be a great teaching aid.