Rear Wheel Wells; Foam Tape For Vibration? Also need help installing heater core

[darkone]

First question:
do i need to use a foam tape on the back sides of the wheel wells where it attaches to the bed? It looked like there was something there at one time when I striped everything. What is an ideal product to use as normal home depot foam tape may hold water.

Second question:
When installing the heater core, do i need to use an adhesion product of some sort to hold the heater core in place? it seems as though it will just be flopping around as it stands now.

any help appreciated. thanks!