Here is a PDI checklist hosted in the forum library. It is for a hybrid camper so some of it is not applicable (like grey and black water). But it still covers most of systems on an A Frame.
Some parts are outdated, like like bringing a CD. Yes spinning music discs are still around, but less and less useful.
One thing that recent A Frame purchasers have noted. Make sure the radio plays both the left and right stereo channels on the inside speakers and you hear both sides in mono on the outside. The outside speaker should be mutable without affecting the inside sound.
Test the stereo by bringing a patch cable and USB cable to connect it to a phone. To test the speakers, it is not that difficult to use software to make a simple track that switches between left and right channels sequentially. But it may be more trouble than it's worth. particularly if you have a MP3 of a song with noticeable stereo separation, like a guitar lead primarily on one side. Or just play Bohemian Rhapsody until the PDI tech screams and runs away.