This kiln was build salvaging pieces from a old pottery kiln. The original interior was  18"X18"X18".  By cutting it down  the interior is now 10"X6.5"X14".  The inside uses the notched bricks from the original kiln.  One could easily notch  regular k-23 firebricks to do the same.  These are 3.5" thick backed up by 1" thick kaowoll.  Which is supposed to have the insulation qualities of 4.5" of  insulating firebrick.  The key is the Bartlett  Temperature Controler.   I'm using the RTC 1000 which is a replacement controller. When I bought it a few years back it cost $175.  I have to say when researching a controller and I came across the Bartlett Co.  I e-mailed them and after explaining my needs they were very helpful and friendly in matching me to a controler.  I have found it works really well.  I'd be the first to admit my kiln isn't pretty but it works well.