I actually considered something like that too. However, I was not able to find any info as to how much compressive force a poly barrel could handle.
I even had a heck of a time finding something slightly official that said they coul be stored on thier side.
I knew I could sit on a barrel on its side without flexing it but, there is a big difference between 185lbs and 900+lbs.
When I decide to move, I can take ALL of this stuff with me.
In all, I expect the rack to weigh a little over 2600 lbs with 300+ gallons of water.
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