I need rain chamber ideas

[flybyferns]

Hi All,
I want to convert this into a rain chamber. ( 36"h x 18 x 18 )
I really need ideas.
I guess I am going to leave the planters in place.
Could they come in handy ?

planters





possibilities for additional tubing ?



upper R has a hole large enough ( in the 'ceiling' ) to pass tubing and electrical tubes for a filter.



I will have to make the bottom completely water proof.

Thanks