I don't know if that furnace is going to improve your mash... at least, it doesn't seem very efficient. Yes, it will retain heat longer, but it will require at least twice as much energy since you're heating the thermal mass of both the bricks and the wort.
I've never had much need for a heated tun. You're much better off just giving it some insulation and a lid. I often don't bother with the insulation and my temp only ever drops one or two degrees during a one-hour mash.