I don't think it would be near this hard for a smaller metaframe as it could easily be heated up at one time with a single heat gun and it could be soaked in a soak tank to remove anything left over.
Honestly though, you may not have to do any of this. If the sealant isn't completely dried out, try just pouring some hot water into the tank. The heat will melt the sealant into a semi-liquid state which will fill any leaks your tank has. After it cools, the tank should be fine. I couldn't use this method with this tank as the sealant was beyond being melted and had turned into something else entirely.