Spent the weekend on the attic hatch and learned a lot

I had the exact same realization last summer when our upstairs hallway was staying at 78 degrees even with the AC blasting. I acutally tried the DIY foam box approach first, but I couldn't get the seal right becasue of how my pull-down stairs were mounted. I ended up buying one of those Attic Tent covers—the AT-2 model if I remember right—and stapled it directly to the rough framing. The difference was immediate. Before the tent, I used an infrared thermometer and the plywood door was hitting 115 degrees. After installing it and adding a layer of Great Stuff foam around the perimeter of the casing, that surface dropped to about 74 degrees. It relly highlights how much of a chimney effect those gaps create. I agree that messing with the roof rafters is a recipe for mold or shingle rot, but I’d also suggest checking the weather stripping on the door itself. I used some Duck brand adhesive foam strips on the inner lip of the frame, and it stopped that phantom draft I used to feel every time the wind picked up.

I ran into a clearance issue with those bulky boxes becasue I use my attic for seasonal storage and kept knocking the cover over. My solution was to treat the hatch panel like a high-performance cooler lid. I cut two slabs of 2-inch Thermax polyiso board and glued them directly to the top side of the plywood hatch using a heavy-duty construction adhesive. To handle the air seal, I skipped the standard foam tape and went with a thick D-profile rubber gasket around the wood stops. I also stapled a layer of perforated radiant foil over the top of the foam. It’s a low-profile setup that doesn't get in the way when I’m hauling Christmas decorations up the ladder. Using my Etekcity infrared thermometer, I saw the surface temp on the hallway side of the door drop by nearly 12 degrees during the peak of the afternoon. It proves you don't always need a massive enclosure if you can get the R-value and the airtight seal right on the door itself.

I'm curious if you've ruled out the hinge hardware as the source of your air leak before committing to those covers? I tried the foam box method myself, but even with a solid seal, I noticed heat was still bleeding through the metal pivot points on the ladder assembly. It’s easy to focus on the door surface, but have you checked if the actual frame of the hatch has warped away from the drywall? Sometimes the weight of the ladder pulls the whole casing down just enough to create a gap that no amount of top-side insulation will fix.