Unless I read the OP incorrectly it sounds like they are just flying through and not staying in Bangkok, the trek to DMK from BKK would be a real challenge, plus DMK is dangerous if you need that flight out of Bangkok and another flooding situation happens like last year. I was trapped in Phuket instead of going to Bangkok because of the flooding, and I was still able to fly through and out of BKK because they have a flood control system that can stop pretty much anything, but down at DMK the airport was flooded almost immediately, in fact NOK had to move operation to BKK during that time.