I don't have any schematic in my hand, but if you have MAX232 and MAX485 connected together, I think this is sufficient to good work.
My other ideas:
- for isolation, use transoptors, and isolated power supply (probably maxim makes IC and smd transformers for this - but I do not remember exact part numbers),
- look at the max voltage on MAX232 and MAX485 line input pins and use transils with that or lower working voltage (ie. lowest max input voltage for MAX232 is +/-15V - use 12V bidirectional TVS, for MAX485 max voltages are: -8/ +12,5V - use unidirectional transils for 7V and 12V),
- use IC's with letter E (ie. MAX485E, MAX232E); they are more resistant to ESD,
- I have used TVS from onsemi, because there are the fastest diodes all over the world
- exact part numbers: 1SMB12CAT3 (12V bidirectional), 1SMB12AT3 (12V unidirectional), 1SMB7.0AT3 (7V unidirectional)