Thank you SoundGuy, think I'll follow the advice WRT to trying w/o fan on exhaust side. It's questionable how long these computer-style fans would last at exhaust temps anyway. Will go ahead w/steel mailbox for exhaust side - think bigger hole/higher flow-through is needed on that side, especially if going passive on that side, with material that can better stand the heat (steel).
As far as intake/right side of box, think this design probably needs a fan there it because it doesn't/won't "properly" isolate exhaust gasses from intake (allowing gen's flow to evacuate box) like some other, more involved/chambered designs.
Hope to get to the mods + assoc tests in the next couple weeks... Maybe:) Otherwise later this summer.
