I have already taken heavy duty clear packaging tape and used that to attach a background. Its nice and wide so it gets a good "bite" on both the tank and the background. The tank I had done that on had the background on it for over 10 years and never pealed on bit. The only thing that I did not like was that even though I taped all 4 sides down to what I thought was pretty much sealed I still managed to get a small amount of salt creep between the glass and background after a few years.
By the way, you question is not dumb at all.