Tank bottom

[Timmy89]

I’m thinking I should put a support under the glass to support the rock since it’ll be 40 pounds?

 

[Bbfishb81]

I have 150 lbs of rock in my 120 and prob 80 lbs of sand, with no issues on having support under it. If tank was build correctly, you shouldn't have any issues.

 

[ndrwater]

You should be fine. Rimmed tanks don't need to be fully supported like acrylic does. The rim does the supporting.
That doesn't mean you can be all Willy nilly and drop rocks in the tank, be careful and methodical. Don't place large rocks in such a way as they can or will fall.