I'm looking into making a jump to both a 10g system and doing all grain.
I can't seem to find any good argument not to just use a cooler if you don't intend to step mash.
Ideally i'd like to be able to step mash so i've been considering a keggle or other pot for the mash tun.
That in mind, the benifit of insulation has come up. Unfortunatly most your heat lost due to convection through the side is on the lower end of the pot and also the heat source. You don't want your insulation to burn.
One ideais a sleave, if/when you fire the burner it will be removed totally
Thinking of using rigid insulation board, 2 layers (stager seam overlaps) The corners of the inside can given a diagnol piece that is vertically scored to curve to make a more round chamber to conform to the mash tun. 'Wall paper' the insides with tyvek. Use a heat resilant mastic.
coordinate the size of it with your brew scupture.