So...super me to the rescue...
* The outer shell is a Polyester laminate (water proof)
* The lining is a very thick impervious fleece by polar tech (malden mills...made in the U.S.A.) and also virtually water proof.
* And for safety, some reflective stripes (I found for 50% off at Joann's a couple weeks ago, thought it would come in handy...and it has)
* Velcro closures for under the belly and around the neck, with a fold over Velcro tab for the wash (like you see on Velcro diapers and covers...to keep the lint out).
I think this should do the trick. Now let's hope I got the dimensions correct. I take it as a good sign that it does not fit my collie. Hopefully, that means it will fit my mom's cocker spaniel just fine.
Maybe next year for Christmas I'll make her a rain hat too...goodness, I don't know if I can't think around those dimensions at this late hour.