So basically like a pontoon boat?
Maybe it's time to try your hand at a new type of welding. You could cut sections out of another drum to make the shapes needed, and then plastic weld the sections together.
You could use a heat gun to bend the drum inward at the right spots, so each pointed end would be made from one drum, and only welded along the front edges. Then you could weld the points onto the drums directly behind them. Worth looking into, no?