<<Now the real question. If I have one of these mini window AC rigs, and
a good inverter, what happens if I set the damn thing on the floor, plug
it in, and take off down the highway? Is this a $77 substitute for
getting my AC fixed and recharged? Will it do the job on the road?>>

This is good question.
And one might think that this would work.
Sounds good to me.
However, what happens to all the hot air and condensation that the AC
unit is pushing out the back side through the condenser?

It will be blowing right back inside the Van as fast as the cold air is
blowing out the front of it.

This would be the merry go round theory and would be self defeating.
The inside of the Van would be like the rain forest in moisture,  off
the coils and the AC unit could never recover from all the hot air it
will be blowing out the back of it.

You must exhaust the warm moist air that's coming out the back of the
unit  outside of the Van.

The newer AC units also use the collected condensation to cool the
condenser down.
The fan picks up the water that the unit makes , and it just gets
splashed around onto the coils to make it more efficient.
They don't just depend on the air being blow through the coils to cool
the freon down.

You'll have a pool of water on the floor of the vehicle that the unit
will be making as fast as it tries to cool the interior down.

So in short;
It won't work as planned ( even though it's a good idea, the AC unit
will be fighting itself to get the job done )

Now, with this all in mind, how do the portable room units work then?

They suck in the room air on one end, exhaust the hot air out the back,
but seem to work pretty good.
The condensation is either collected in a drain pan ( which has to be
dumped every so often ) or is run out a tube to the outside somehow.

I wonder how they seem to work pretty good with re-using the hot air
that is being blown out the back?
Where does it go?

This is confusing.

But I do know that a window unit won't work the same way as the portable
floor unit.