I just tried veggie oil on the last backing I put on my 150g. It looked real good. It's just like RTR said. It looks brighter. Like it is in the tank. Also it made it alot easier to work with (aligning & all). That is how I'm going to do all my tanks when I get around to it.
ah, your welcome Randy....like you I am sold on vaseline.... can't believe the difference and the adherence value... it was a miracle work for me and I see you have found the miracle too that's not such a bad thing, huh...
Here is another trick to get an even better finished look.
Get a piece of the plastic wallpaper corner protectors (sold in Home Depot or similiar stores for a buck or two). These form a right angle and are about 1/2" or so wide on each side. They have self adhesive strips on them. I put them on the back corner of the tank - so they overlap the tank background on the back and the glass on the side.
you just need to measure and cut one to length. Then you have a complete finished look on the back where your background is.
I just used tape on the black construction paper I have as my background. It works fine, I can't see any tape because I did it on the base and the rim, not the glass. Never had a problem with my little tank or the big one.