I read this book about this guy who used to fish Dillon Reservoir at night with a streamer and bubble and just nail monster browns. I forget how he rigged it, but I do remember he used a VERY slow retrieve. So it seems like if there are browns where you're fishing, night time could be good.
Some of my biggest fish have come @ night in a float tube slow retrieving streamers, wooly buggers, leeches and the like with a flyrod. If not a flyrod, try casting or trolling rapala's close to shore...I'd think slower is better, but the fish will tell.
Night fishing in a float tube will require a white light visible in all directions, depending on the body of water. That presents some problems with fly casting...you'll need to mind your backcast a bit more.