Wow, wow, wow. Thank you, Thank you everyone- This post and all its replies saved me a lot of pain, and just in the nick of time. I am building an oven similar to the one PeteH shows in his picture. I dry-layed the floor last week and was about to start laying the mortared walls this weekend. I was going back and forth regarding ceramic board vs. concrete/vermiculite. I went with the vermiculite. Then I read this string yesterday. Instead of mixing mortar next, I am going to pull out the floor and add 1" ceramic (thickest I can fit now) under the floor and around its perimeter. I have a box-like, Roman/Greek decorative enclosure planned (think Parthenon) and it will allow me a lot of volume between the firebrick barrel and facade to fill with ceramic blanket and vermiculite. I also have planned a removable door cover with adjustable venting and an adjustable damper at the top of the chimney.
Now for the ridiculously ironic part--- My name is also PeteH and I also live in Connecticut. If it wasn't for the posting PeteH's picture of his oven, I would have thought I was in the Twilight Zone, reading a post from me in the near future regarding the oven I screwed up.
Thanks again everyone, I have put a lot of time and effort into this oven this summer and I would have been heartbroken if I did not get good temperatures in it. Please if anyone has any other advise on modifying this design while in process, please tag on.