We had a demo on using tissues with white glue/water mix last Friday night at our club meeting on making tonneau/bed covers on pickup beds. I didn't watch the demo as I was busy gabbin' with other members. This method could be used to make tarps over engines, cars, etc. as well.
If you're having problems like that with your decals, I suggest that you spray the decal sheets with a couple light coats of clear lacquer and let them dry for 24 hours before using them. This should cure the problem I hope.