Here's what you need:

16 x .187 Wall Gray PVC Duct Pipe Type 1 Grade 1 : PEP Plastic, Specializing in Plastic Engineered Products

Would have to set down with you and get a total weight figure to determine pipe diameter. I figured 16" in 2-10' Lengths would float 800 pounds leaving them half out of the water, but you may want to get by with less, and use 12-14" (12" being just shy of 500 pounds), but those weights are total flotation=boat, gear, and gewber.

Don't know, a 10' Jon Jon is only 100 pounds:

TRACKER Boats : Riveted Jon & Utility Boats : 2013 Topper 1036 Riveted Jon Description

And I bet you could find a beat-up used one for a coupe Bills. The 2 PVC floats will weigh that much alone. Only reason I'm taking this route is because I've got no other options, and is why mine will be a knock-down design so I can handle and stow it.