I just got a 1989 E-250 Coachman and couldn't find any manual. Like my other Class A, C and TT there probably is not a manual that would be worth anything anyway.
You might get a Chiltons or Haynes manual for the vehicle part of the Coachman. You can also look online for each of the appliances, water heater, AC, Fridge, etc. and collect them digitally.
I've collected them for all appliances as well as photos of instructions on furnaces and the like.
Good luck and enjoy the search. You'll learn alot while hunting.