I would stick with Aerospace 303.
I’ve had 2 tonneau covers in the last 15 years and 303 has done an amazing job. My covers have held up from freezing snowy weather with salt over roads to the high heat and uv of the south.
If I remember correctly, Access Cover my brand, recommends 303.
Edit....I was talking with a friend of mine who owns a boat. He reminded me that 303 is very popular with boating enthusiasts for protecting various items on a boat due to its stout UV protection capabilities.