These are just the parts I used to attach corflute parts together and brace them, though that bracing is not really required, i just used old corflute with many preexisting folds so it helped. If you grab 2 sheets of 3mm 1200x900 corflute then suggested cut pattern is attached. the enclosure for an A1 i went with 500mm wide, 650mm high and 620mm deep. I added a space blanket to mine with double sided tape and packing tape, with an internal temp of 35C and room temp of 23C the insulated parts were 26C and the uninsulated parts at 33C. So it makes a difference. 
One of the rivets is for stitching corflute together, the other is a pin that goes through the corner brace and 1 or 2 sheets of corflute to retain it. the edge bracing slides on and seems to hold on ok. They are ugly as i want them fast and easy to print and i simply dont care :) Just print them flat for strength.

With an A1 bed at 100C  it went from 23C to 36C in 30 minutes with a few air gaps I later sealed and an uninsulated front door. 

created in onshape at https://cad.onshape.com/documents/fa8ca6db06f0ebd1b0f00869/w/e690aa1d5f8bfd54faa37c0e/e/27047531272b4a92996d93d8