Max input 13.2V means you should pick a TVS with that as the peak maximum voltage. Which is going to be more like a 9V rated diode. Which is perfectly fine for a 5V system, and can still be powered from, say, unregulated 5-7V DC adapters.
A unidirectional TVS will also cover reverse voltage protection. For both reverse and overvoltage conditions, you might want to add a polyfuse*, a regular fuse, or a fusible resistor.
*Polyfuses take forever to "open" (~100ms), so that your circuit won't really be protected from damage. In that time, the TVS will happily cook off and fail shorted (and maybe burn out and open up again, who knows). There are combo TVS+polyfuse devices out there, which use the TVS to heat the fuse element: it opens faster, protecting itself.
Polyfuses also need the fault current to be limited to a safe value, otherwise they'll blow open (a monofuse
). With some shopping, you can usually find a device with the right current rating, and enough minimum resistance, to handle that without adding external resistors.
If you wish to give the RS-485 additional protection, I'd recommend a 6 to 12V bidirectional TVS for each line.
Tim