Thank you for the input. We’ll definitely incorporate a ballast structure. Typically, there will be 2 people and a Polaris (I use it as legs but it’s a blast, too) but I want to allow for those times when the kids come to visit (large family, 4 generations, rambunctious sons – I think we had 18 people for Thanksgiving last year). Anyway, we’re designing with 12 people in mind and I am thinking that using barrels (or series of) as an external ballast may just work. The idea is that we could just empty and fill as needed –any thoughts? Again, thank you – you all have been extremely helpful.