I used white formica glued in place and sealed the seams with silicone. Worked really well initially, but the glue failed over time due to the humidity inside my canopy, and the formica bowed out away from the wood.
I had bad luck with polyurethane varnish in the past.
Then I lined with white formica--type laminate attached with ss pan head screws and sealed with silicon seal. It held up for 15 years and was real easy to clean. But the laminate kind of expands after a while. I also did not seal it to the rim and salt/moisture creep expanded the wood behind the laminate.
Last year I replaced the wood hood with a top built out of white sheet PVC use for outdoor trim (and therefore UV-resistant), welded with regular PVC glue and sealed to the rim with silicon. I was worried about heat from the MH but so far so good.