[Hondaracer]

I think you’re on the right idea with the lumber and a flashing

The stupid vinyl siding has such a large step down it’s very hard to do anything with it unless you’re gonna to all custom and use the vinyl J trim to frame it out etc. especially in areas where it’s hit with a lot of rain.

Once you do mount it I’d run a nice bead of weatherproof silicon around the fixture before the final mounting