you're correct, and all of my comments are assuming the hole is sealed by the tow bar mounting bracket. I retract my insult to the engineers (for this 4 inch section of the frame only, they still suck on the overall frame

). My frame has been sealed back there since I bought it which created the trench, with those giant holes you've got back there, there's no need to widen the rear holes as I've done. I'd still widen however on a case by case basis as I'm sure many others have unwittingly plugged that hole up - the prior owner installed the tow bar on mine & it has those bolt plates (?) that you fish in to secure the rail which completely covers over everything.
I actually have an endoscopic photo that lit up that entire inside section showing what mine looked like but damn if I can find it; here's the outside though:
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This area in red would probably hold a half cup of water. And if you're in the salt-belt make that a half a cup of brine. I've seen more of these sections rotted out than I can count around here.
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