Installing tonight. Debating which sealant to use on the stove connection and top plate seal. I have mill-pak. Will this be ok. Have seen on this web-site some use high temp mortar. A local dealer said that basically anything i put in there will eventually harden & crack in a short period of time. Is this true? One better than another? Should I put a nice bead inside the stove exhaust prior to dropping the stove connector in, or should I drop in, secure connector, and then just run a bead around seam? Can I use mill-pak to seal top?