We have been using 55gal totes in the 'ALBO Pepper' fashion with great success;
https://albopepper.com/30-gallon-tote.php
Using 6" corrugated pipe, our resevoirs hold ~10gal of water.
2 55gal totes fit perfectly in a 4x4, but they work great outside too.
Solid for 4x4?
I am going to try the 55gal totes, have those too and after the small pots I used for my peppers and tomatoes last year anytime it was remotely warm I felt like a babysitter. There is even a tote sitting a half mile away in the bush someone left that I am going to re-purpose. Thanks for the concept ATP!
If your aunt had balls she'd be your uncle.