More specifically to your sealing problem, you can do better, but it'll take some work. IMHO, ideally what you would have are bulkhead fittings for the stuff that needs to cross the boundary of the ice chest. For the tubing, you place a closed-cell foam between the bulkhead fitting and wall. Then you connect your tubing to the bulkhead fitting and clamp it on each side of the wall.
For the wiring and evaporator lines, you run them through a clearance hole and then seal both ends of the hole with an RTV sealant like silicone. This stuff isn't exactly permanent, but might as well be. If the thought of encasing stuff semi-permanently in silicone isn't appealing you can also get fittings for running the electric cord through the wall and sealing it. Options abound, each with its own advantages and disadvantages.
For the final lid, you should also have a closed-cell strip that you clamp down with ~5 lbf/in of seal length. Having a nice smooth surface for this strip is important.
The way things are now you've got a highly variable surface from the polyurethane foam.
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