You did the right thing Scott. You don't need to put it in the water too deep. The Tandom axle on an 18'er will float some from the tires, and I've seen that happen on a steel trailer too. The frame has holes in it from the light wires etc, but you can go under the side rail of the frame and add a few holes to bleed the trapped air in the frame faster. Don't think it will help a great deal, but might help some.