I run into this issue of PHP Error: Class ‘App\Trailer’ not found in Psy Shell code on line 1 and this is how I had it resolved.
How to produce Error
You may likely get this error when trying to work with a particular model in tinker. This is not a problem with your code, so don’t go messing up with your code in an attempt to fix this.
Here is what to do, simply dump-autoload files and let the composer rebuild your autoloaded files. Exit tinker (if you’re currently using tinker) and type this into your console
Wait for the code to finish running, then open tinker and trying doing the same thing that was leading to this error again. Problem resolved.