Definitely sounds kinda cool
While it would have some challenges, it would achievable for sure.
if you think about the weight and structural requirements 500kg is not a lot really. If it is supported at four corners, that's 125kg per corner, not hard to deal with at all.
I used to have a 350L fish tank on a stand, it just sat on the floor boards in the lounge room, with no issue at all
can you take a pic of where it would go? draw a sketch of what you are thinking?
edit: ooops, just re read the OP and see that you cant take a pic :lol:
I don't think your sketch was there when I first read it either?
I would look at trying to incorporate a sump type filter system into the tank if you can conceal it.
from your little sketch, the weak points in the tank design are the two bottom corners, all the weight of the water is pushing down and outward with the most force at the bottom of the tank.