I have a big problem with heat pouring in from this attic access point in my closet. The board doesn't sit flush all the way around, maybe a 1/2" gap around part of the board. I live in Houston, TX, so it can get quite hot during the year. Even keeping my closet door closed doesn't always help plus it would be nice if my closet wasn't an oven. Does anyone know of some good products I could use to seal that gap up so the heat stops coming through. This isn't the only way in so it's not a problem if it's 100% sealed for good.

copy below link to see what the board looks like if you need to.

imgur.com/X2jce

Thanks!