Nice build! I doubt you'll have a problem with the flashing ( unless you get a giant grease fire for a long time) I've never had a problem with mine.
As for a way to sear/grill, get some more of the 1ftX2ft expanded metal from HD, cut with tin snips the length wise into 3 to 4 inchs tall, bend into a simple circle and bolt together or weld. Make the circle a bit smaller than your second rack dimension and just lay that on top of your second rank, light a full weber starter with coals, dump into that circle (with unlit coals depending on how high of temp and how much you want to cook). Put in your top rack and go at it with your bottom vents wide open. Works great. This one has been thru many many cooks and still going strong with. Also I started with a 2 inch bottom of the barrel hole with a slide adjustment. Used 1/2 of a soup can with holes in the sides of the can to let air in and no ashes to fall out of the smoker inside covering that 2 inch bottom hole. When doing long cooks, the ash would cover the holes in the can and snuff the fire out. So I went to side vents. Never had another problem.