PET containers for freezer meals?
Not all PET plastic are microwave safe; make certain the containers you buy are labelled as such.

see this link.

"Unlabeled plastic containers aren't necessarily unsafe for the microwave. But the lack of label just means that these plastics haven't gone through the battery of tests required to ensure microwave safety. Because there's no way to tell if these containers can hold up to microwave heat, it's best not to use them in the microwave."

and this; 

"Many of our manufactures do not recommend HDPE for the microwave and we suggest that you avoid it unless the manufacture has specifically approved it. PET and polycarbonate should not be used for microwaving as they tend to absorb heat."