It's pretty clear that the symptoms the OP reports, i.e. CO alarm going off and foods taking twice as long to bake, that the mouse nests cleared out of the oven are only part of the blockages. The entire oven needs going over, especially the burner and the air inlet thereto.
This is NOT a minor issue. Carbon monoxide kills. That's why there is a CO alarm in the first place. Do not assume the alarm is faulty. Check out carefully that oven. Do not attempt to cook other stuff until you've cleared up the issue, and for certain, do not stay in the rig while making the first batch of goodies after you think you've gotten the oven straight, just in case. This is a matter of life and death.
