Water Skeeter makes an M3Day Tripper that is a "pontoon" float tube. Sit up out of the water but no oars. Supports 350 pound person. $149 and weighs 17 pounds.

I think it is the same one I have seen on Orvis and Cabelas web sites. But to see it you can go to:
oregonfishing.com
on top menu bar.."products"
left menu bar.."Kick boats & FloatTubes

You will see two. The Backpacker Lite supports 290 pounds and the M3 Daytripper below it supports 350lbs. Click on "more info" in the text of each boat to read more.

Gem