303 washes off in the rain, per a call to manufacturer regarding outside use. I do use the stuff on my tires because it doesn't affect the anti-oxidation compounds in the rubber.
As I posted somewhere some years ago, there is this stuff Marabu Classic Clearshield, which is a UV inhibitor for professional use on vinyl graphics. Not sold on Amazon etc., only from pro-suppliers like Lexjet. I had to use my company name to order, but was able to pay with credit card. It is $30 for a quart which is way more than you will ever need. You put it on with a brush.
A review here: https://signs101.com/threads/liquid-laminate-for-latex-printers.143736/