Plastic Grill Housing Repair

I believe you are talking about the black piece that the egg crate portion fit onto. That can be repaired with fiberglass as I have done it. It's not a ideal situation to only apply to one side but it does work and it doesn't see too much wear and tear. Unless of course there are pieces missing in which case you have a bigger problem. I simply glued the two pieces together with cyanoacrylate (crazy glue) to hold it in place after I roughed up the underneath. Then carefully applied 3 or 4 layers and let it set. It worked fine. The crack is barely noticeable.