IF any of you decide a Hot Knife is a better way to cut ,then allow Me to caution you and ensure you place a small fan behind or beside you before doing so . Cut outside or in your garage use the fan ,as it smells and can be toxic !.
I regularly have used a hot knife for decades as well as heated platens ,so as to emboss cavity's into various foam matrix .
Advantage it's QUICK , CLEAN AND SEALS as it cuts thus eliminating fraying or pop outs . Putting something into a recessed foam and removing it has a tendency to tear or fray foams . Especially padding or upholstery type foam . We all know there are several grades and types of foams .
Another trick is after cutting the foam is using a material **to cover the foam ,adhering with 3M super 90 spray adhesive . It also serves a very useful purpose . ** Automotive upholstery or heavier drape materials work well . I did #2 of MY cases out of Cordura ,as I had a bunch left over from a project . Tip leave material long enough in the cut outs so as to adhere on bottom side of foam .
Cordura can be bought for as little as $7.00 a yard or less .