303 will work, to some degree.
I would seriously look at dingy chaps. These are covers, typically made out of sunbrella or other outdoor material. They are designed to cover the tubes almost completely. That will sure cut down on UV!
As for the potential for separation from the RIB floor, if it happens, glue it back together! I've heard 5200 will work great. Of course it will never come off, but...
Are you taking the engine off before lifting to the fordeck? You can get a dingy engine crane mounted on the stern corner that will lift the dink engine, then you secure it to the rail. THEN, you hoist the dink, or tow it.
Whatever you do, try to avoid towing with the engine attached. Even in calm conditions, you could get waked. Flipping the dink is one thing, loosing the engine is a rather bigger deal!