Also the glass itself weights a bucket-load...
If you do think the two chests could take the weight, i ould recommend a large sheet of plywood at least 10mm thick between the chest and the tank. This shouls disperse the weight a little bit between the two.
Its not that hard to build a stand that will take the weight - just lots of 2x4 with plenty of support. Or for the simple bug ugly approach, just use breeze blocks and plywood