Tristan's hearing aid has been found! I can't tell you how relieved I am to be able to type that out.
After the fiasco with the stash in the car, I tore apart Tristan's room. He had things stashed all over the place. I cleaned his toy box out. I hit his closet where I found dirty laundry and a huge stash of soiled pull ups.
Tristan still wets the bed. We don't make a big deal out of it since he's on medication that really knocks him out at night. We put him in Good Nites to make him as comfortable as we can while he's sleeping. It also cuts down on laundry and reduces damage to his bed. We've tried to just let him go to bed without the Good Nites, but he sleeps soundly til the morning regardless. Being wet just doesn't wake him up.
Anyways, I pulled everything away from the wall and went through every square inch of his room. I finally found the hearing aid stashed behind his toy box. I was so relieved to find it. We checked it out to make sure it was still working, and it was just fine.
I made him clean out all those disgusting Good Nites and explained for the umpteenth time how gross it was and that I wasn't mad that he wet the bed, he just needed to take care of it. I really wonder what's going on with this hoarding-like behavior.