I paddle with a skin boat guy reguarly who uses regular spar varnish. He thins the first few coats to penitrate the fabric (canvas) - than puts on a few more coats - done. He has built three with this finishing method and has no complaints. Tommorrow I'll put in a picture of it. What brand? - anything! He finishes it off with non-gloss so it's not shiny. He uses a garden sprayer with the wand to spray the inside with Thompsons or once again ... (anything that's on sale).