BED Need help.

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Just started to do my 2nd 72 4x4.I blasted the the inside of the bed and found rust on the last cross member and on the floor ( on the corners). This is to be expected I know. I then ordered a patch panel with visions of cutting in a nice new piece. The problem was the the patch panel it never matched the contours on the bed floor. Is there an approach to fixing this area or does anyone have a really nice long bed for sale? This bed is really solid except for this area. Any suggestions would be helpful.