If your hatch rests directly on the moldings add 2 1 2 inch wide stops around the opening.
Air sealing details for attic hatch.
Seal the attic access.
Weatherstrip the attic access hatch or door.
The stops provide a wider surface for attaching the weatherstrip and a space to mount hook and eye fasteners.
Cut 1 3 boards to fit the perimeter of the opening and nail them on with 6d finish nails.
Apply self adhesive foam weatherstrip tape to the top edge of the stop.
Gaskets are generally more durable and produce a tighter seal.
The standard air sealing recommendation is to install a compression bulb weatherstrip.
This can also be beefed up to a sealing gasket like the one on your refrigerator door.
Air seal the hatch perimeter the plywood hatch rests on a small wood strip lip.