Well Papa...I read through the site and studied the 'above ground-cinder block-aluminum foil- metal grate' method, and it looked like a lot of work! Admittedly, a fun way to stay the heck out of the women's way 'inside' the house, knocking back several six-packs, but work nonetheless!
I think you've really got to stoke up the Caja China's to first heat up all that metal, and then have it transfer into the box itself. And even then it may not be 'all that.'
At my church (yes, I said church) we've got a huge in ground affair with concrete blocks, gas piped in to heat up rocks, and then bury the 'quarry' under burlap bags, etc. I always figured a few hundred years from now some paleontologist is going to dig up the remains and figure we had human sacrifices or somesuch!
Thanks for your referral to the 'Cuban-Christmas'!