First off don't but cheap decoys such as Flambeau or Carrylite, if you must go plastic G&H is the way to go. Use a decoy bag not the mesh sack type but real decoy bags that are made for that purpose.
Second don't shoot you decoys! I read that post I had to chuckle to myself. I wouldn't use any type of coating. A glossy shine on your blocks doesn't look natural from a distance, I see so many that throw decoys to set them in cold weather and end up with a coatiing of ice that shines like a mirror and then wonder why they can't pull birds.
If they need touching up it is best to buy paint and go that route.