Paul,
No worries, this foil is only going on the inside of the wood chassis so it won't interfere with ventilation in any way.
I'm also building the amp on a 10" x 12" chassis and I'll be adding some extra ventilation slots as well. A friend of mine is going to lay all this out in a CAD system with me telling him where things will go in the larger format, then we'll just take the drawing file and plate over to the local water-jet place to get the plate cut. I was going to try to mill the whole thing on my drill press with a cross slide table, but decided against that. :-).
-- Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)