Here are the boots with their styrofoam insulation soles firmly attached with "NO MORE NAILS" construction adhesive ....and I've filled in gaps with the stuff as well and allowed it to dry fully....over 24 hours. I was then able to carve away all the excess styrofoam to shape the soles a little neater.
Remember you MUST cut a wedge out of the soles at the toes where the meet the floor or you won't be able to walk without the soles tearing off! You have to be able to roll your foot forward when you take a step! Try them on and you'll see. No more than and two inches or so need to be trimmed back.
Then I got some black vinyl upholstery fabric and cut a strip long enough to wrap around the entire sole from heel to toe. Make sure you leave some overlap which can be trimmed off later. Try to match the fabric with the bottom of the sole, but leave extra at the top which will be trimmed also. Once again I used "NO MORE NAILS" to attach the fabric to the styrofoam.