I think the 2004 models, and maybe the 2003 models, have an inside switch just as you describe. It is an improvement, but you still have to remember to switch it off when you break camp. If you simply unplug the shore power cord, drain the water, move to another campground, and plug in the shore power cord, you will still burn out the heater element.
The switch on my 2002 was outside, which annoyed me. I installed an inside switch, but I went one better. I installed a "special" inside switch that automatically switches itself off when the shore power cord is unplugged. Then, at the next campsite, the heater stays "off" until I push the button to manually turn it on. And the need to turn it on manually reminds me to fill the water first. Absent-mindedness is no longer a problem.
The "special" switch is easy to build, but requires electrical skills. If you want to try, drop me a line.
Bill