Thanks for the flour tip. Duly noted.
Having made two consecutive meatloaf dishes that were squishy, I concede that adding the same ingredients that are meant for the topping into the interior of the loaf is a guarantee to have squishy meatloaf... delicious, with a somewhat unique flavoring, but structural lousy for making a meatloaf sandwich.
I make my meatloaf with fresh breadcubes, 1 egg, 1 onion, salt & pepper, and put ketchup on the top. Bake 1 hour, 350-degrees. Drain grease. Delicious.