I just sold my travel trailer. The person who bought it found dry rot on the back wall. He wants his money back. We did NOT know it was there. I am obligated to give him his money back? He is now taking me to small claims court. Wouldn't this follow under "as is" laws>>

Did you sell it "as is "? Anything in writing?

No, nothing in writing..

Hard to say without anything written. Not sure he has a case unless he can prove you purposefully hid the damage. No matter what I sell, guns, cars etc, if used, I always mark it "as is"
"Firearm / car etc., etc., is bought/ sold /traded AS-IS, with no warranty given or implied. Buyer accepts all risks in owning and operating this weapon/car etc and agrees to hold harmless the seller from all and any injuries arising from the use or operation of this weapon/car etc.".

If you sold it as a travel trailer, is it road worthy? Is inspection required for this class of vehicle in your jurisdiction?
If it is not fit for use on the road due to structural deficiency, it could be a problem for you because it could be deemed not a travel trailer as claimed by you and/or implied warranty if applicable.
That might be his approach and he can easily say there was no "as is" discussion if not on bill of sale or any separate written statement of the type ma0641 described.