Hey FS a bit of advice for you, I know there are going to be some on here that will not agree with me but here it is, fish with one rod!
I use to take 3 or 4 different rods out with me on my tube and found that they tend to get in the way more than you would think. Fishing from a tube is nothing like fishing from a boat! You have very limited space and trying to cast or fight a fish with all the extra rods in the way is a big hassle not to mention you run the chance of losing a setup! It has happened to me once.
If you really want to take an extra setup out with you then buy the rod holder made for float tubes....BPS sells a nice one for about $20.
http://www.basspro.com/webapp/wcs/st...005000_175-5-0
Decide on what fish finder you want to use and I will help you come up with a way to rig and mount it.
sonarbp