Another approach would be to build an isolation box to put your amp into. If you have a separate cab (think 4x12) then just keep the head out side the iso box and just put the cab in. If its a combo amp then then only thing you need to worry about here is the trapped heat inside the box from the amp. There are ways around this but a simple solution is to simply only have the amp on while you are playing/recording. This is alot cheaper than trying to engineer a sound proof room (quite complex and expensive) and also easier on your ears in the long run.