What a strange coincidence. I was just talking about FSX@War’s SE Asia package - Vietnam circa-1968 -ish. A Mudspike link to the package here.
I developed the Haiphong Harbor/CityAirbases and the Cam Rahn Bay port facilities. Haiphong is pretty accurate as I found a good US military map on line from 1968 and was able to rectify it to to ADE to use as the underlying image of the area. CRB was a bit more speculative but is a good “feel” for the area at the time.
You need TACPACK and FSX/PD3
Definitely a sandbox vs campaign or mission oriented. The MILVIZ F-4E and/or F-100 for TACPACK are really must have’s for this package. (RAZBAM put out a TACPACK A-7 just before went all DCS…cal it an early Beta…but it does work…I’m not sure you can get it…eBay?) The F-4E can “double” for a Navy F-4J so you can do Yankee Station stuff.
Hmmmm…can not reach the RSX@War server…and last Facebook post is a year old…are they gone the way of the buffalo? 
EDIT: Evidently yes they have, as of last year. But the base packages, are still available for download over at the VRS TACPACK forum.