Restoration: 3 Truck Bed Bodywork Questions... (w/ Pictures!)

[Springbear]

I am in the full swing of things! I am running into strange looking repairs under the truck bed.

1. Where the rear cross sill is rusted it was once "beveled". To what purpose was this? Someone previously has covered with a bed patch this area. What was originally there?







I also found a "sticky" gasket material under the wheel housing. What should I use when reassembling?



Thank you for your help!