I found a site that has the water shield for about $20.00. Since the problems with the electronics for my windows started after the first heavy rain subsequent to a "repair" (and after the engine light came on for my oxygen sensor; but I'm going to call that one a coincidence), I'll assume that having a decent water shield is important.

Can I rig up a water shield with thick plastic (body bag) and adhesive or do actual water shields have additional properties I want (heat proof, etc)?

Thanks
MRR

 

That window drop relay was on the outside of the watershield, so I don't think that your trashed watershield was the source of your problems.
If you can get the right part for 20 bucks, just do it. It will be a lot easier to put on and you'll be a lot more satisfied with the result.