Is there a product to seal a box type fan to a steel building, approximately with 1-1/4 ribs and I'm guessing 22ga. panels?

There isn’t a specific off-the-shelf product to seal a box fan to ribbed steel panels; most installs use a wall housing or mounting frame with foam closure strips or sealant to match the rib profile and prevent air gaps. For your setup, it would typically be a custom-fit solution—feel free to share your wall details and we can help recommend the best approach.