I am thinking of using the spray basting on a wall idea. I haven't before due to allergies. It was suggested to tape the back to the garage door, spray and put the batt on, spray the batt and add the top. I think I might be able to do that since it will all be outside. I will have to wait for nice weather to try it.
I have been using the Hobbs 80/20 fusible batt and I do like that. I put on knee pads and iron it on the old carpet in the basement. It works really well with no puckers on the back. There are lots of options to try, good luck!