I had a similiar problem this week on a new door I put in my metal building. You can buy a grey rope type foam in a few different diameters that you can use to push in the spaces around the frame to seal it off from the air and critters. I used that packed fairly tight and used caulking to fill the last of the outside gap.
The spray non expanding foam works good to, but it sure can be messy and damn near imposible to get off anything it comes in contact with, so use with caution.
You could also use a piece of 1/4 round trim on the outside after its packed with the foam, painted the same color that may look a little neater then the caulking.