bliomey didnt think you could still get polywarm rugs!! i used to use a stetchy on a polywarm and duvet combo many moons ago! Have you got a handy saddler handy that could stitch cross overs onto rug?
Actually I don't think you can still get them, it's one I unearthed when looking for rugs for New Pony (it's a bit too close to Christmas to justify buying new rugs) don't know how old it is, but it's still in great condition apart from no surcingles
I've got one too and keep meaning to have some made for it. You could either ask your saddler/repairer to make full cross surcingles so you only have the fastenings on the near side or have double fastening ones made like they were made for; I always used to find that they opened too easily with their double ones and if you have one that rolls a lot, you're likely to find rug hanging around the neck instead! Failing that, a good roller instead completely!