I forgot about the hose bed issue. And sure, you can add compartments but that defeats the whole purpose of the rear mount which is a small, compact rig.
Originally posted by BC79er
It would depend on whose rear-mount to pick and how you build it. Of the few I've seen, there are a couple that seem to pick up space if done right. The Pierce rear-mount at Dallas in 2003 had a ton of space because it was built with a 500 gallon tank. You do lose one whole compartment to the pump panel at the reat, but you can make the body a little longer than normal. Usually you end up with 4 compartments per side instead of 3 if you keep the length of the truck the same as a side mount. The pump panel area becomes a compartment, and you keep the rest. ALF's can be rearranged too. Can't find any good pictures right now. I haven't seen too many other people jumping on the rear-mount wagon.
They do make for a real high supply line hosebed, but if you normally have hydrants nearby and only use a 25' or 50' section, then they can be kept in a compartment so you will rarely have to repack supply line. And if you do, well that's what rookies are for. :p