Sources of clunk / rattle under the van?

Hi all, new here. I have owned this little Toyota Liteace for a couple of months, cousins with US van you could say. In this van (2WD) is a coil-sprung rear axle with multi links. Since day 1, I have been trying to track down the source of a clunk, which is in the back half of the van when going over bumps.

So far have addressed the following issues:
- new rear shocks which were sloppy / rattly
- adjusted rear hatch latch to prevent door from shaking
- new tires as a matter of course
- chased down and fixed various wire harness mounting points to prevent the harnesses knocking inside the body
- have put my hands on and wiggled about everything I can find in the rear half of the car
- front sway bar bushings (unrelated)
- replaced all three motor mounts (was getting rubbing on crossbar)

Next on my list to check:
- gas tank mounting straps
- give the spare tire carrier a closer look
- ?

Running out of ideas here. Its entirely possible my efforts at finding a loose joint by hand are just not going to work, maybe need something like a crow bar?

Attachment 7930

Follow up, crawled around under there a few days ago:

- gas tank straps tight
- spare tire carrier tight
- verified exhaust cannot hit on anything
- tightened the speedo cable which could thunk against the gas tank

Noise is still there. I'm still suspicious of my rear hatch. The body seal is FUBAR, and the lip of metal it attaches to is corroded away in places. I can't really duplicate the sound by shaking on it, but it does have a lot of mass. The van has no interior panels in it, so I have already stripped out or battened down anything inside the walls that could be shifting.