We bought a used Bell kevlar canoe a few years ago. The gentleman we bought it from sent a spray bottle of 303 Aerospace Protectant with it. I used the remainder of the bottle on the hull over the past several years. Now that bottle is gone, I'm wondering if there is anything better to clean/treat and protect from UV damage or if 303 is pretty good stuff.

This is what Rutabaga replaced 303 with.... UV Tech

I do like "303" and find "UV Tech" almost if not identical in performance and application.
Most complaints center on it's short life after treatment and the way it can wash off in the water.
I find it easy to use and the results, even if short lived, are worth it.

butthead

Is the 303 or other similar products necessary? I clean my boat after each use and keep it in the garage. I have used the 303 but have not been diligent in applying it.

If you store indoors and are worried about greater protection, get or make a sock for your canoe, transporting it is the next biggest time sunlight and other objects would prematurely age it.
How much time does it spend in the sunlight when used? Most of the time it is the interior, which will get a lot of wear so whatever you use, it has to deal with that probably more than water. So something that is water resistant for the exterior, something wear resistant for the interior.
To me it is more trouble than it is worth.