I fired up the oven and had it going for 5 hours. But the oven floor was fairly damp and outside temp around freezing. The oven never got hot. Any thoughts?
When was the last time you used it? Do you have a picture of your oven with the veneer? Do you have a roof?
Most likely it was damp and you need to go through another cure to drive the moisture out.
I think the answer was in your question. Cold outside plus excessive moisture. I agree that you should do another cure to get the moisture out.
Mine got soaked in a couple of monsoon events on Christmas Eve and New Year’s Eve. The mouth of the oven was protected, but water poured down the sides of the dome and absolutely drenched the framing bricks around the hearth. They can and will wick water inside. I’ll have to do a complete set of curing fires when the weather allows, and I will also be waterproofing the framing bricks going forward.