I know you cannot use poly as a weatherproofer, but can you use them as a combo? Poly then waterseal? Poly for shine and watersealer for outdoor use? Thanks!
Use outdoor poly. It has UV protectors in it. I use outdoor poly for both indoors and out.
First, apply the exterior sealer,
then followed by an exterior poly or spar varnish.
The number of finish coats, as recommended by the manufacturer of the product, you chose.