I don't think room temp is a big deal. I think they're saying don't do what I did many years ago: I forgot my cast iron pan on the stove and when I remembered it was actually so hot it was glowing. I grabbed it off the stove and stuck it in the sink and ran cold water over it to cool it down...CRACK!!!!!! It was immediate! So I was stupid, in my 20's, what can I say?
Our dutch oven worked great. I followed the directions for burning off the wax coating. then scrubbed it clean and dried it on low heat. I used Olive Oil to season. There was a website and I will have to see if I can find it again that listed all the smoke points of different oils. It was recommended to use oil with a high smoke point and to season at high temperature. Olive Oil has a high smoke point. I ended up doing 2 full coats and heating, the first didn't seem to set in certain spots. The 2nd turned out good.
I do have another question though I read several places that said that your cast iron should be pre-heated. So I did pre-heat and everything turned out fine. But I have also seen warnings to not put cold liquid in/on heated cast iron? We made stuffed peppers, so tomato paste is used and it was at room temp. Could we have put all the food in the dutch oven and then put it on the coals? Or should we pre-heat both the oven and the ingredients?