Your post's always crack me up.....Randaddy.......No sugar added......none needed.
Cool set up. A guy brought one like that on a Deso trip. The wattage of the amp and volume you play it at will equate to the battery life. His battery lasted about 4 days and we played it a lot. It was a garden tractor gel type battery if I remember right. It was low water and we needed something to drown out the motor noise of our party barge.....and I'm in the group that likes music to float to.
One thing I would add to the design is a cigarette type power outlet mounted inside or externally....... for charging things like I pods, GPS's or whatever in camp.
I still take my old Dewalt AM/FM radio that has an external plug for Ipods. It's pretty much water proof as long as you quickly dry it out after a flip.
The batteries last four or five days of steady play and are not that heavy for the length of play time they give you. Six would probably be enough for a grand canyon trip. You could probably cut that in half by using the new type of batteries they sell for them these days.
I bought a Memorex Ipod dock that folds up nice and small and sound really good for what it is. It's not water proof at all but perfect for in kitchen and dinner time music. Easy to move around the kitchen. It runs on AAA's and I usually get about 20 hours out of a set of batteries. Here is a link to the model I bought. I think I only paid around $40.00 at a K-mart in West Virginia.
Memorex PurePlay Portable Speaker System (MI3602... : Target
It makes for a great back up system.
Of coarse...... maybe we can all agree ......that the best music on the river is .......live music......usually at night......around a camp fire.
Enjoy your trip and crank it up in Redwall cavern. That will be a true test of your new system.