L Channel / Corner Angle for Shower Bulkhead

[crabbey1]

Hey guys!

I am almost done with my bathroom renovation. The shower bulkhead wall has been reinstalled but it is too think to use the original channel where the wall meets the aluminum panel walls. I tried using an aluminum L-Channel but it doesn't bend smooth enough for the curve of the wall. Does anyone have any sources for plastic L-Channels? It needs to be flexible and waterproof.

Thanks for any ideas!

Chris