Well, I'm assuming you'll be fishing light line (10-15) inshore plastics and stuff, so I'd suggest one of Pete's loomis' that he likes. He'll have to fill those in, cause I don't know the models off the top of my head. They're popping rods I believe. I use a castaway STH7 for a lot my float tubing, look into that. I bought mine from Pete, see if he's got any in stock, or if he'll order one for ya. They're pretty cheap too ($125 or so). A 300 size reel may be too big for this rod (what are you gonna fish on that reel? 20?) so if it's a 20# stick you're after, look into some calstar models. The 800XL will work nicely. Some folks don't like fishing long rods from the float tube (I prefer my bass rod just cause it's easier to deal with), so if you don't want the 8 ft. stick, try the 700xl, or the best of both worlds, a thin diameter, long loomis rod. It's long, but not as beefy at the butt, so it's easier to handle and stuff (I'd imagine). Check the swr108-20C. Also, I recently found on bad-fish.com that they have a sweet blank called the swr 114 or something. Apparently Jamon (remember that guy...) has one and it's a sweet stick. There's another one to look into. As a general rule, for a 20# stick, look at calstars, seekers, and loomis.
-Brian