Snagly,
Bill Herzog had a tip on this very subject in the February-March issue of Salmon, Trout and Steelheader 2000 magazine. He says.....to grind the bottom of the boot fairly smooth, but that some roughness is desired for better bonding. Next pack the boot super tight with newspaper, so that you can barely depress the boot with a hard squeeze. Then, go to the hardware store and get some Barge brand all-purpose one-part cement (look for the yellow and red label) and a roll or two of elastic black electricians tape. Using a small disposable foam paint brush, slather the bottom of the boot with a generous amount of cement and then immediately do the same to the felt. Wiat about 10 minutes for both surfaces to become tacky and then line then up and press them together. Starting at the toe, wrap the tape around the felt and the boot (this is why the boots must be packed tight with newspaper) until you have covered every inch of the felt up and down the boot. Don't worry about the excess glue oozing out. Let the glue cure like this for 1 full week before un-wrapping them. Sand the excess glue off and you should be good to go!
I hope this helps!
Randy