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I did buy an after market gasket for mine when the old one rotted away. When it's hot or in the sun, the new one falls out way too often. I gotta do something about that. I'd glue it in but have seen what glue fumes do to plastic. Any ideas?

I don't know if this would work on a Pelican box, it would depend on the way the gasket is engineered?

On my plastic snap-lid food boxes, I made a homemade silicone gasket by applying a bead of clear RV silicone/sealer and then covering with a sheets(s) of plastic wrap. You then snap on the lid and let set overnight.
You get a very serviceable gasket. You can use a razor blade to trim any excess squeeze-out after it dries. You have to wipe plastic with alcohol wipe to prep before applying silicone.

I'd maybe experiment on a plastic coffee can or something similar to see if it would work okay on a Pelican box, but it held up on the food box for 2 years and might be worth a look :-/