Hello,
I have the original Interstate group 24 battery. Since the TM is a 2006, I'm guessing that it is at least two years old. I was actually surprised by how well it held up. Along with the heater fan, I was using one or two lights, and running water which kicked in the water pump.
That's a good idea about charging the toilet beforehand and bringing an empty 5-gallon container. In fact I believe I have a collapsible 5-gallon container that wouldn't take up any space.
I can't say enough good things about the privy.
http://beprepared.com/product.asp_Q_pn_E_CH%20S100
That link also has the solar shower setup which you've mentioned.
I'm into buying things that are easy to set up and take down and this can be done in less than a minute. I've attached a picture. The thing I need to do is to extend the length of the outdoor shower hose maybe by having a quick-connect fitting. The only downside is that you need to get the hot/cold water adjustment to your liking before going in. I like the pop up concept so much I also bought a 10x10 pop-up screen house.