Just a quickie. I'll be staying at my GF's rented apartment during the 90 days I'll be in Thailand pretty soon. My question now is, who should inform Immigration of my whereabouts? Her or the apartment owner (who doesn't yet know I'll be staying there)?

Offcially you shuld inform immirgation that you stay there and the landlord also informs immirgation but he has the option to do it at the local police station.

Your own reporting is not informed, reporting by commercial landlords is now enforced and he should report you to the police.

Offcially you shuld inform immirgation that you stay there and the landlord also informs immirgation but he has the option to do it at the local police station.

Your own reporting is not informed, reporting by commercial landlords is now enforced and he should report you to the police.

OK, so he should submit a TM.30 form presumably?

And mine would be the TM.28 flavour, correct?

you just write it on the form when you enter the country.

You only need to notify again if you move ito another non-commercial home.