I have an older house that I'm in the process of repainting. This house is single wall construction (common for older homes in Hawaii) with lap siding.

The previous owner did not install a corner board and I would like to install such so that I have a trim to paint (to help give a break in the color).

Is my only reasonable option to simply nail 1x3" strips to the corners and fill in the triangular gaps with caulk? Any help would be appreciated.