Wow, thanks for the link to rvsurplus...It would almost be cheaper to buy those than build my own after epoxy, materials, ect.... Definitely something to think about!
The reason I am going to do tanks instead of bags is just for the simplicity in changing from wake to surf. I really like the way Ralph has his boat set up and I am trying to mimic that. You can move the pop bags (or whatever you have up front) to the back corner quickly and easily. You couldnt put all that weight on top of sacs, but you can with tanks!