It is possible to connect RS2323 via optoisolators without having to add an isolated power supply.
The IRED in the opto can be driven directly by the MAX232 with a suitable resistor in series (say 2k2). Cathode to GND.
The phototrt emitter can be connected directly to the input of the other MAX232. And the phototrt collector can take the supply voltage from a modem control line such as DTR. So, you must set DTR active (+12V) as if it were a "receive enable" signal.
For a duplex connection, add a simmetrical circuit.
Sorry, it is difficult to describe the circuit without a schematic diagram.

Regards,
Alfredo del Rio.