Looking forward to that Tony.
Been to Spotlight -no luck but they did have maybe similiar - Helmar Crystal Kote -says it is for drawings,artwork (I reckon backglasses are rare artwork),prints,photographs,documents.I dont think this will do any damage,will bite the bullet and try it. Will report on outcome.

I've used Helmar Crystal Kote due to lack of triple thick. OK so far possibly not as thick as the krylon but I put three coats on.