I made a duct from some previously used stainless over the weekend and installed it this morning. The fan will blow air down from within the duct, causing air to be pulled from the back portion of the oven. This duct is really rough, being made from previously bent, then straightened (sort of) sheet metal. I ordered some new stainless sheet from ACS to fabricate a new / better one in the future.

Substantial improvement. We're down to about 35 F differential between fromt and back, which, per the heat treating spec is not quite good enough.

Later, it occurred to me that the differential may be affected by running the oven on 110VAC instead of 220VAC. I designed the controls of the oven to run on either 110 or 220VAC, so it should work OK.

Hrm, my 12V power supply was dropping out when run on 110VAC. Should be fine, but it's a cheapie from China via eBay. This is actually the 2nd one...the first one was worse.

I was able to prevent the 12V supply from dropping out by temporarily disconnecting the cooling fan for the electrical enclosure. Started doing a test run, but had to stop due to my extension cord getting hot. You see, this garage only has a two 110VAC outlets wired, and they're both 15A outlets. Grrr. So, unless I want to rewire the garage outlets, I have to run an extension cord into the kitchen to plug in to one of those 20A outlets. But of course every extension cord I own is 16/3, so not suitable for even 15A current draw. Ordered a new, 12/3 extension cord on Amazon. Also a NEMA 5-15 to C13 cord...the one I ordered is 14 gauge, which is slightly too small, but should be OK.