If all you need is a water tight seal for basic environmental conditions, I would suggest a closed cell foam product frequently a silicone or urethane.
Your deflection is a function of the reaction load of the gasket. By decreasing the reaction load, you will decrease the deflection.
If...
Polyethylene and Polypropylene are the two most difficult materials to stick to due to their low surface energy.
3M has a 9495LE Double coated product or 9472LE transfer adhesive which is your best bet.
There are several electrically conductive adhesives with aluminum, copper, and gold carriers that are available by several different companies.
Things to consider is galvanic interaction between the conductive carriers to avoid rust and corrosion issues. You also need to know the amount of...
