I just bought a tank from CL, the guy had his background attached with an oil, I am almost 90% positive it was vegetable oil, he told me I could use vinegar or something to remove the oil/clean the tank.
Oil is deff the way to go, it adheres to the glass very nicely and none of that sticky tape mess... just oily residue afterwards if you ever take it off... and that's easy to wipe off.