I've found some surface rust on the inside of my 240Z's hatch, mostly at the bottom.  It seems that water was in there at some point, but I don't see any signs of recent ingress.

 

 

Should I leave it alone, or spray the inside of the hatch with Rustoleum?  Do something else?

 

 

If you leave it, it will continue to rust, if you spray it with rust paint it will be hidden but continue to rust, same with oil or wax sprays.  The easiest way to get rid of the rust is make up a dunk tank or bath with 2x4's and a waterproof tarp that is deep enough to cover the rust.  Then fill the dunk tank with a solution of water, citric acid and table salt and drop the hatch into it.

Citric acid is available on Amazon, you only a 1 pound, let the hatch sit for 24hrs pull it out and rinse it with a garden hose, if it needs more time throw it back in for another day.

I assume I would need to pull the window, seals/gaskets, badges, etc before it goes into the dunk tank?

According to how far you’ve got to submerse it I would think

3 hours ago, woof said:

I assume I would need to pull the window, seals/gaskets, badges, etc before it goes into the dunk tank?

I shouldn't have, but I assumed if the rust was that bad the hatch would be off the car and you would be repainting anyway. If you are trying to keep the paint then you can't dunk it, you'll have to resort to phosphoric acid based rust removers.  They work but can add complications especially with painting.