I was shown how to cut about 1/4" off the inside edge with a new razor blade so it fits the rim perfectly.
Straight edge cuts not beveled.
Mount the foam on the rim, flip your tire inside out, line up and place the inside/carcus up against the foam.
Squeeze the tire, foam and rim tightly together with four fingers inside the tire and your thumb on the bottom of the foam/rim then stretch the tire over the foam while still holding the four fingers very tight on top of the foam and rim.
It'll pop right on with very little practice and the foam won't get bunched up.
Check the outside edges for fit, seat the bead easily cuz the foam won't be in the way since you cut it just right
. Now just pull the bead back and glue it.
Works for me and the uncut outside edge fills out the tire tread nicely.
Thanks to Mr. Hartson, Stevens dad for this tip as well as many others he kicked down at So. Cal.