Just got back from Savannakhet. Multiple O for Marriage was easy. The only doc the IO studied was the original red-bordered marriage certificate. A grand total of 7 pieces of paper submitted. Only down-side is that Savannakhet may be the most boring town in Asia.
TLDR : Answer Summary
The user reports a smooth experience obtaining a Multiple O visa for marriage in Savannakhet, submitting only seven documents, including an original marriage certificate. There are discussions in the comments about financial documentation and personal experiences at accommodations nearby, along with varying opinions on the potential increase in visitors to Savannakhet.