Does anyone have a suggestion for a GREAT polyurethane for outside?

Varathane. Works on boats in the water. I restored an old wood table 40 years ago, use it indoors and out, looks the same as the day I did it.

Varathane is a Rustoleum product and generally just polyurethane made for raw wood not painted wood. Most exterior painted surfaces don't need a sealer. Sealers are made to be absorbed into wood and not lay on the surface. There are very few products for sealing exterior painted wood surfaces. For added protection, Minwax Polycrylic is a clear acrylic product with polyurethane resins. These resins protect the paint from moisture and duress. This coating bonds best with latex paint.

I would look for some type of marine polyurethane. It's meant to withstand harsh weather/conditions. Good luck!

Thank you

Thank you, very informative.

Thought about something like that but can it be used over water based finishes?