Again, sensible space gain in a small home is 10,000 Btu/hr when trying
to maintain 80f db and 60% rh under an ambient of 105 DB and 65 WB.
This challenge neglects internal latent gains to simplify things and
lets consider sea level elevation.

A few problems with using an evaporative cooler to treat indoor air in
doing this. 80 db & 60% RH would have a wet bulb temperature of close
to 70F. The ambient air has a wet bulb temperature of 65F. The wet bulb
dictates what the supply air temperature can be, and treating the
outside air CAN provide, if needed, a supply air temperature almost 5
degrees F cooler than treating indoor air will allow.

If your down under data was in fact treating indoor air only, it still
seemed like the wet bulb was constant, and if remarkably they did not
run the exhaust, then there probably was farily high infiltration
occuring, keeping humidity down. They were up against some pretty
insignificant conditions at night as well, low 80s fairly low RH, so
it really proves squat except there is a wet bulb angle that your
missaplication of physics never accounts for.

When you treat the outside air, you are pressurizing the home with cool
air, and must provide pressure relief whether a dedicated opening or an
envelope with the integrity of swiss cheese. This will over power any
typical natural infiltration and cool air will be leaving the space.

Treating indoor air only will have to allow for natural infiltration
which would be in addition to the 10,000 gain, but you will end up with
a steady exhaust fan running and the space will be negative with
respect to outdoors so infiltration will be ruled out and you would be
dealing with the make up air volume into the space instead.

The make up air adds heat directly to the room air. The exhaust rates
will be higher than you initially think. In fact the exhaust will cause
the amount of air to be treated by the indoor unit and the water
consumption to increase. As per our last arguement on this subject, you
will find the airflow and water consumption to spiral upwards from what
your physics say.

You will be using two fans with the indoor scheme, move more air, use
more water, plus when you put the amount of make up air into
perspective of a small home, the amount of hot air rapidly infiltrating
in will feel like a sirocco wind. The solution to this problem is to
duct the make up air right to the evap cooler. Suddenly comfort will
increase, exhaust rate required drops, the amount of water needed drops
and on paper we have a system that works.

So what the exercise will prove is that you can put the swamp cooler
inside but it still works the best when it directly treats the outside
air. So outside of some effects of the sun blaring on a box on the
roof, you will find that there is no benefit of having the cooler
inside.

I will check back in a week or so, to see what you come up with