Savannakhet is the easiest. Drop off paper work in the morning. Pick up your passport in the afternoon of the next day.
I will mention this. There has been some problems with them asking for your wife to be there with you. The other day, there was a post about this. Some in line were asked some were not. If he is able to have his wife there with him, I suggest he does so. If not, I would have him get his wife to write a letter stating she wants them to give him the multiple entry non-o. Also, have her prepared to receive a call from them to confirm everything.
it all comes down to the IO, which I’m sure you’re well aware of. Tod has a perfect list which did list the letter on it. I would suggest any and everyone follows that list.
I’ve been preaching this requirement for months. The majority of the people laughed at me, said it wasn’t a requirement. It’s better to be over prepared than be rejected because some IO wants to nitpick.
Technically, there’s no limit by air. But you’re eventually going to be pulled aside by the immigration officer and questioned why you’re spending so much time here via the exemption stamps. You can keep rolling the dice. You’ll soon roll snake eyes and end up denied entry. I would suggest you start entering with the proper visa. A lot less hassle and a better chance of not being stopped. I would also suggest you have everything in order when you arrive. Proof of accommodation, 20k baht (or equivalent currency) cash and an onward ticket out of Thailand within 30 days.