Would I have been better off not knowing?

I would probably hammer form a piece to go in that trunk floor and cut that stuff out. Not hard to form a piece of 18g over a block of wood You can buy that lower trunk tub as opposed to the whole trunk floor. I've tried the weld it up method and don't care for all the grinding of the bird turd welding on both sides and grinding the whole thing paper thin again trying to blend it in.