I can think of several reasons.. But first.. The one that works for me.
if it's raining out I use the indoor plumbing in this class A.. Oh, that's not the problem you had.
Ok, for one thing I am a diabetic with neuropathy,, (nerve damage due, in my case, to the diabetes) a side effect of this is that when I got to go, often I got to go NOW!!!,, No time for that hike to the head.
Another reason, at least for men in many areas, is that Freeway Rest stops in some areas are well..... Man flys into DTE (an airport) rents a car.. Asks for directions to the nearest rest area (happens most every day at DTE) and (this does not always happen) Finds the potential homosexual partner he was soliciting was actually a working man.. and his job is LAW ENFORCEMENT OFFICER.
So he wizzed on the tire to avoid dealing with those inside.
Now.. side effect of what I used to do for a living (Dispatch those LEOs) I know which rest areas to avoid, at least in that area, but .... This hetrosexual male deals with it differently. (I use the motor home head.. Simple, what?)
MAJOR advantage of a class A.
