Just to add, you need the back and front copies of the rose boarder Thai marriage cert signed by your wife. The back has a stamp from the local Amphoe on it.
The kor ror 22 isn't needed, just a signed(by your wife) copy and the original(returned to you) rose boarder marriage cert. You'll need any foreign marriage certs translated into Thai and certified by the MFA.
I've had about 7 or 8 of the multi-entry non imm O visas from Savannakhet and never taken the wife with me or had an invitation letter from her. It's never been a requirement there. It's not an argument it's a fact!
Yes, I've had that visa about 6 or 7 times from Savannakhet, it's exactly the same documentation as the single entry Non Imm O but you just tick the multiple entry box on the application form and pay the extra 3000bt.