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.
I'm feeling bearish, and I'm packing a Wusthof Grand Brisket slicer from MABA
"I'm Armenian...perhaps...but then again...maybe not..."