Jim,
I think that "challenge" is just for those of us who have a tag axle. Do you still have the original, giant-trashcan-sized, muffler? One of Steve's primary reasons for changing to the Aero 5050XL (and now Magnaflow) was to improve battery access. Barry has some great photos of the difference on his site here: Exhaust System Replacement - 2003 U320 (http://www.beamalarm.com/Documents/exhaust_system_replacement-2003_u320.html)
along with an overall discussion and multiple parts lists here: Replacing the Muffler with a Resonator (http://www.beamalarm.com/Documents/replacing_the_muffler_with_a_resonator.html)
Yes, I even considered removing the muffler to make it easier to install the third battery.
I installed two from the side, but the third I had to install from the rear. I made a wooden ramp that I hooked to the battery cage and used a small bottle jack to lift the two batteries up so I could simply slide them into the cage. However, the third battery could not be done that way since the muffler interfered. I learned a lot, so would do it differently if I ever have to do it again. What a STUPID design! Foretravel gets an "F" for this "feature".
We don't have that setup on our coach, but I had heard that the whole battery tray can be lowered with a jack after removing support bolts.