[Steve Neul]

Use only the spar varnish and be sure it's a marine grade spar varnish. The polyshade finish is an interior finish. You can have a paint company add come color tint to the spar varnish to make it work like polyshades. Just keep in mind that adding anything to the finish other than thinner will weaken it. If they won't do it you can mix a brown exterior oil based enamel to spar varnish. Just add it a little at a time and test it on scrap wood until you get the color you want.

 

[Steve Neul]

If it were me I would do the stripping with paint and varnish remover and a power washer. It would do a more thorough stripping and make for less sanding. Remember sand is a four letter word.