I know a lot of modelers don't like this, but a hobby glue gun at low temp has worked great for my needs.
I used Glidden Gripper primer sealer to butt joined the 2x2 blue foam to make a 4x8 sheet.I've searched this site and others and came up with tons of products to use. The most common problem is the availability of adhesives or styrofoam glues. Liquid nails LN 604 seems to be a decent one, cant find any locally. Same with the Loctite PL300. "out of stock" I'd like more options/ideas on what you have used. How did it work and is it available? Amazon has the Liquid Nails at $24 a tube ( 10 ounce). It's like they know its hard to find and they are gouging the public. For comparison, Home Depot sells the PL604 at $73 a case (24) 10 ounce tubes, when its available. about $6 a tube. So I could use some other ideas. thanks