[Mikendebbie]

There are lots of threads on that subject. Based on what I have read here (not personal experience) - someday I intend to add support to all of my tanks. Forum member Rohrman has some excellent pics of some support he added to his tanks (don't remember if it was black tanks or gray or fresh water). He added some angle iron cross members (2 or 3) below the tanks bolted to the main frame beams and placed wood between the angle iron and the sloped bottom of the tanks (sort of like shims). The job can only be done with the coroplast bottom removed.

This is on my to-do list. Until then I travel with very little liquid in any of the tanks.