It's motivating to sunscreen your kayak before a trip, whether it is plastic or fibreglass. I have one of each. For me, it's the only way to get motivated, otherwise I keep putting it off. And I know on a trip, the kayak is going to spend a lot more time in the hot sun. But, it's important to do it properly. There are several different brands of product to sunscreen and protect your kayak. I used Aerospace 303.
The kayak also looks beautiful after a proper cleaning and treatment, sometimes even showroom ready. And, I feel better when I'm tripping knowing I've given it some sun protection. It also reminds me to bring my human sunscreen too.
Here's a link to my article on sunscreening your kayak and how to do it properly according to the manufacturer's instructions.