Hi George, Ive been thinking the same i guess I'm governed by the top opening which needs to be about 12" diameter
I was thinking, after I posted my previous message...I cobbled together my own 'liner' rather than use a proprietary clay pot. A proper clay pot would probably have a smaller internal volume and should therefore be easier to heat. Also, my insulation was poor or non-existent, so heat escaped, I guess, and couldn't build up. I only achieved about 300C; some 200C short of my target temperature. I'd be interested to hear of the temperature achieved by anyone else here.
Anyway, for my next attempt - this summer perhaps - I'll be aiming for a cavity which is just large enough to accommodate one naan bread and one or two rods of chicken tikka. The cavity doesn't need to be any larger than that for my needs - cooking for no more than 6 people. You could still churn out half a dozen naans, one at a time, and should have better control. More importantly, the running costs should be less, to get up to anywhere near 500C, whether you're using gas or charcoal.
If I was buying a ready-made clay pot, I'd probably buy the smallest one which could take one naan bread and one or two rods of chicken tikka. I agree that the opening needs to be large enough or it would be very difficult to use.