It sounds like this has been an ongoing issue...never heard of urethane foam used as a slide seal. There are dozens of seal designs, so it's hard to address your exact problem or suggest alterations. To better it, look at some seal suppliers or get advise from an RV repair tech.
When we have high, sustained (+50mph) winds, rain will come in at a few lower corners of the slide. The seal is not much more than an large, exterior rubber squeegee. There are no interior seals that compressed when the slide is extended. I am not impressed with the method/style the manufacturer used to seal our slides. We didn't have leaks with our previous TT's slides under the same conditions.