I'd say this is a common problem with most makes. How serious varies. My solution was pretty easy and worked well for me.
I cut several pieces of 3/4" plywood that I could slide underneath the empty tank and above the angle support to brace the bottom of the tank.
The I screwed through the rail into the plywood to capture the plywood. Just use screws that don't go through the plywood.
then in several spots I screwed 1" wide 3/16" flat stock into the rails so the flat stock replaced the thin bands.
This supports the water tank well.
If you don't have clearance to install 3/4" plywood, use thinner if possible and if no room at all, use 1 1/2 or 2" 3/16 angle iron in multiple places screwed into th the rails. In fact you could sandwich plywood between the rails and the angle iron. The plywood distributes the weight so the tanks doesn't deform.
2011 Keystone Outback 295RE
2004 14' bikehauler with full living quarters
2015.5 Denali 4x4 CC/SB Duramax/Allison
2004.5 Silverado 4x4 CC/SB Duramax/Allison passed on to our Son!