Rick, are the barrels sitting in the saddles?
Or bolted?
They are bolted. That is why your top barrel needs to have a removable ring/lid.
Water running down your pipe to the barrels is your only concern. It will rust out your barrels. (My buddies did). That is why I ran mine out the side and the barrels are holding out nice. Once you get a good fire going, refill the bottom barrel and shut the vents down.... Your good for 12-15+ hrs.
Even though my buddy's barrel rusted out....All components were reuseable and he just built another one.