I would agree with using the slim backgrounds, I had the Malawi Rock style, and although it looked good, it took up a lot of space in the tank. In some places, it was a good 7" thick. After a while I removed it and shaved a bunch off.
It is also very buoyant, and unless it is secured tightly will float.
The first time I installed it in my 150, I tried to use heavy rocks and C-clamps, and once the water was back in, it shot out like a breaching whale. And it left spaces behind where fish could hide, and die, and a pain to get out.
After shaving off thickness, I cut it in quarters, and filled in the cracks with Great Stuff "pond", pic below is dry

old shot in tank with young menerambo
