I have a fibreglass tank. Unlike the bottom of a glass tank for instance, the bottom of a fibreglass tank can have slight imperfections in it. Mine was meant for outside and the manufacturer said it would be wise to sit it on the floor on a bed of sand.
But of course I wasn't planning on having mine outside, it was going in my indoor fish room. So I built a 12" tall stand out of 3x2's so the viewing window of the tank would be elevated. I threw a sheet of ply on top and finished it with a sheet of 2" thick styrofoam. This would help with the imperfections in the base of the tank.
No need to push the boat out regarding fancy filtration either. I have one of those huge blue HDPE drums at the side of my tank with a four crate tier trickle system within it.
This tank has been set up since June 2019 and neither the stand or the filtration system has caused me any concern whatsoever. If I got another fibreglass tank tomorrow I'd set it up exactly the same way.