What can I use to trim this gable end?

The roofers for the previous owner trimmed the gable end with 12" wide hardboard (Masonite), which of course completely rotted in a few years.

The exposed siding is T-11 which leaves grooves behind the aluminum flashing. Not good. So they put thin board from the higher roof overlapping the flashing. It was a smooth, clean solution.

I cannot find thin board that is PVC or composite.

- The space tapers from 8" at the ridge to 10 1/2" at the eaves because of a slightly different roof pitch.

- the shingles extend 2" beyond the original siding

Some options I have considered

- 3/4" x 11" x 8' thick composite board cut to fit, join the 8' lengths.

- 1/2" thick treated plywood. Does that stuff take paint?, trimmed with 5" wide composite board

- 1/2" x 4' x 8' Azec sheet composite, which is $100 per sheet, ripped and cut to fit, trimmed out with Azec composite or PVC 5" wide