Wonder what the chances of cutting a scab out of a donor truck bed in the junkyard is and welding it back over the hole there. Then you just have a weld seam to deal with, which could be hidden easily enough.
It would suck to have to scrap the old bed or have some kludged up sheet metal patchwork.
There's got to be a hole in the cab, too.
Alex, you have some work to do! You need to keep the tonneau cover on to keep water out of the cab.