So I went to HD this afternoon. I was going to get all the lumber and stuff I needed to make 6 of these frames, but I decided to just get enough to make 1 and do a test run because I haven't done any of this before and wanted to be sure it came out okay before I go and buy a bunch of lumber.
I was initially going to make them 2'x4' because that is the size that the insulation comes in, but I decided to make them 2'x3' because that is the ratio of many movie posters, and 2'x4' is pretty damn big!
I used 1x3's of pine. They were close to $5 for 8ft of it.
So I got 2 24" pieces and 2 36" pieces. Initially I was going to use the 24" pieces as the "outer" pieces, but ended up making the 36" pieces the "outer" pieces. And it sucks because after my initial decision, I ended up cutting 2 22.5" pieces to use as backing of the frame, since the insulation is going to be 2" thick, and the frame is 2.5" thick, I was going to put 2 bars of .5" across the back just to support the insulation. But since I initially was going to only need 22.5" lengths, I cut 2 of those, and now I need 24" for the 2 back pieces, so I ended up not being able to use them, which sucks because those pieces were paid by the foot and it was nearly 4 feet.
Anyways, I ended up buying the corner clamp things, some nails, and gorilla wood glue. I put glue on the edges and used the clamps to keep them in place, and while drying, I hammered 3 nails into each joint.
I think they came out pretty well so I'm probably going to get the lumber to make more of them, and also make sure that I actually cut the back pieces 24" this time