In completing a trolley from a wood kit, my painted finish efforts on the roof only continued to accuate the wood grain. This was after a sealer, and spraying with clear acrylic lacquer. My car restoration instinct led to a product called EVERCOAT brand Polyester Glazing Putty. Mixed with a Home Depot sold red cream catalyst, this very fine grain putty spreads soooo smoothly and fills the grain of the wood. It does not cause the grain to rise per the fluids of lacquer or sealers. The outcome, after a 400/500 wet/dry grit sanding and light application of a spray can primer, was a metal-smooth finish. No grain showed after two coats of spray can high gloss black epoxy. I used the same technique in eliminating wood grain in restoring a rare 1912 Model T wood body Tourabout.
Evercoat makes a large number of finishing products obtained from automotive finishing suppliers. The Polyester Glazing Putty comes in a small can and if kept sealed will last for years.
Wendell