Independent of all methods described in your answer, is it not adequate to seal the cooking vessel with heavy aluminum foil, and then repeat the closure a second time? Thank you!

Shalom, Thank you for your question. In the issue of how to cook milk and meat in the same oven, there are many opinions amongst the rabbis. You are correct that a fully sealed pot in an oven (and certainly one with two wrappings of foil on it) will alleviate all problems of cooking milk in a meat oven, or visa versa. The rabbi's answer was addressing the more common situation where the food is cooked in regular pots without this double-wrapping. Blessings.