Here's the hole with four pieces of wood that Lisa screwed into the ceiling as a frame to hold a trap door.
Lisa inserted four combination wood screw-bolts onto which the door would fit.
She then cut a piece of plywood to the right size, drilled holes in the right places, put weather stripping around the edges (just barely visible here) so it would seal tightly, and stapled ceiling insulation onto the upper surface. I didn't take a picture, but she also put a piece of the R-30 ceiling insulation into that vent from the living room to further reduce heat leakage.
Finally, she lifted the door into place and secured it with wing nuts. This should close off the hole (and significantly reduce heat leakage) while also still allowing access to the ceiling space when necessary.
I didn't take pictures, but Lisa stuck the small camera (the one she used to record this year's WSFS Business Meeting) into the ceiling space, allowing us to have a look around without having to poke our heads into the space. There are two ceiling vents (this picture is of the outside east wall of the house) as there should be, but now they won't be serving as direct conduits to pour heat out of the living room and kitchen.
Lisa feels pretty pleased with herself, and I don't blame her. Later, she plans to paint the trap door and put a handle on it. I'll probably make a label for it that says something like "WARNING: Undoing wing nuts will cause door to fall straight down!" to warn anyone that there are no hinges on the trap door.