Bigger water bowl and deeper substrate on the cool side (eco earth IMO) the deeper cool side substrate can be wet under the surface generating a large water reserve to slowly release. Tubs are ok at holding humidity but the big issue is heating them with out heating the room they are kept in. Hot side temps are easy but cool side and ambient air temps with tubs are hard, there are few options and the solution for 90% of tub users is to keep them in a room that is, or, is close to 80ºF. If you are able to do this they are a decent option if you cannot, they are a poor option.