Johnny47 yes, true thing. I'm still trying to figure it out myself too, but I think it all depends on who u meet at the customs, in the end. I think most won't pay attention to this aspect but if u find the annoying one, then better to have a valid sub while going back and forth Thailand (even just that month, not necessarily 6)
Johnny47 if it's only for getting the DTV Visa, I think u can even do only the first month of sub, if u wanna do specifically 6 months instead, better to try to contact local gyms directly or check their prices and compare them, directly. Gmaps can be helpful to find those, based on your preferred location