i know some of you guys built trailers. question is is what is the order to paint wood. i mean like do i first do waterproofer then primer then paint, or just primer then paint. how would i do it.

Kind of functional and personal opinion-depending on type of wood, ply or solid planks, personally I would stain the tone I wanted and cover with coat of Minwax PU in semi gloss or flat , if you want colors, then prime, paint -using a exterior latex-where glow fuel might be spilled - add a coat of PU.

JMO I'd start with a wood sealer, instead of waterproofer and sand - another coat of sealer and sand - then stain and Minwax PU as per (flipstart). I would rather use an OIL BASE over LATEX - JMO