Trunk cover plate insulation

what is everyone using to seal the trunk cover plate located in the trunk? it seals body openings above the differential.
ed

Seal? From what? Water can’t splash that high. Mine’s just screwed down. If anything minor airflow might be beneficial.

used to seal out

moisture, heat and fumes from entering trunk.

I intend to use just a thin sheet of closed cell foam after carefully painting all surfaces to prevent corrosion. The only time it will ever be seen again is when the rear suspension is dropped so it is not really a big deal as long as it is sealed.