Okay so follow with me here:

Smell of propane (yeah I know not propane but odorant. People who tell
you that buffaloes are really bison and geraniums are properly called
pelargoniums should be ignored, too) outside the van, not inside.

Shut off main valve from tank. Smell persists. That should narrow it
down to tank, filler bits, and input half of valve. What if valve does
not actually shut off completely? Open stove valves to drop pressure in
low-pressure line. Close stove valve, wait 24 hours. Open stove valve
again -- if pressure is heard, then main valve ain't doing its job. In
that case, the leak could be anywhere.

So my next test is to confirm that the main valve does what it is
supposed to do to help narrow the possibilities.

And that would answer my original Question #1.

In the meantime, here are the two questions that remain unanswered:

2. The autostop valve's reset button -- I'd like to try to reset it,
but pushing on it as hard as my measly fingers can does not move it. Use
a tiny hammer? Hire a gorilla? What's the trick for pushing that thing in?

Which leads to:

3. Could the autostop valve be the source of my propane whiffs?

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR