I ran into the same problem purchasing a used travel trailer- no overall vehicle documentation. But an online search of individual components of the vehicle turned up rich sources for PDF copies of what I needed. Write down your make, model and sometimes the serial numbers for the big chunks of your trailer - refrigerator, stove, propane detector, heater, A/C, water heater and the converter battery charger - and whatever else that might matter. And simply search by make and model number to see what turns up. Then I killed a few trees and printed them out for keeping in a binder that goes with us when we travel.
There is a very good site that had most of the manuals that I needed but I can't find the link to it. I will track it down later today on a different computer if you need it.
Edit: Found it!! Search for a company called "PDX RV Wholesale". They are the Library of Congress for RV individual component owners manuals.
Rick