I would go with a piece of 1/8" or 3/16" sheet stock, cut into a triangle, or my preference, a truncated triangle (trapezoid) that is welded on each side of the vertical to the frame. The truncated triangle is welded such that there is a triangular gap at the 90 degree angle from the frame to the verticals. This prevents build up of grease in that corner.
me: I don't drink anymore
Yelonutz: me either, but, then again, I don't drink any less