Call me Captain Caution, you wouldn't be the first, but I think I'd invest in a couple of good quality ratcheting straps to tie each barrel to the frame.
And I would definitely not maiden voyage this thing without backup, meaning another boat.
Weather can come in on you amazingly quickly and a little wind could easily defeat you from going the direction you want. I've sure been blown across a lake in a flat bottomed canoe a few times.
Seriously consider a centerboard or leeboard. With your design it would be easy to drop one down that center slot once you're in the water. That would help your stability tremendously.
This thing really does need a small spinnaker. Not much because of the flat fronts on the barrels, but enough to have a little fun with.