Has anyone here tried the 'doble-doble' double mash single liquor approach?

I am preparing to brew my first truly BIG beer, an RIS at 1.100 or thereabouts, and I am thinking about trying the 'doble'doble' approach outlined in Radical Brewing. Essentially you split the grainbill in two, mash the first half, and then use the resulting wort as the liquor for the second half of the grain bill (and sparge as normal afterward), reheating to strike temps and dumping in the fresh grains for a second mash.

I am interested because it seems like a great way to conserve space and concentrate the wort without having to boil for 4 hours (I only have a 7.5 gal boiling pot). My only concern is that it seems like it would be a waste not to rinse out the first grain bed before re-loading the mash tun.....anyway.

If you have tried this, please tell me how it worked out. If you haven't, can you see any big holes or hidden problems in the idea? thanks!

I have actually thought about doing something VERY similar to this for the upcoming 10-10-10 brew. I think you'd suffer efficiency by not sparging the first mash at all though. Maybe reheat the first mash and sparge using that before moving on to the second mash? Or maybe figure the volumes so that you have separate volumes of mash and sparge water that both get reused. you'd have to have two pots though...

Sparge the rest of the grains and keep it for a small beer or starter. I wouldn't waste what is left in the tun.

David