Ceiling repair

[coryhynes]

Hi.
I had a leaky spot in my ceiling. I repaired it by replacing with foam insulation and hardboard using adhesive. Along some edges I was able to use small screws to support the board. However, on some corners there is no metal to screw into. My question is, how do I support these corners with no metal frame to attach to? Any help would be great. (see pics)
Thanks

[coryhynes]

Here is the finished product. Used wall paneling for the ceiling. Looks ok and serves the purpose.

[deartruc]

Impressive. Nice job!