SuperDarly

This mission fits what you describe very well. It's MP co-op but I've hosted it as a LAN game and played it solo. You can set up defenses, buy units for your squad, AI commander will give you missions randomly or when you request patrol ops. Enemy AI will capture and recapture town, patrol areas, etc... If you are good with SQL you can set up a database that saves the mission progress so you can keep coming back to the same session over and over (or let the mission run in a dedicated server setting and it will keep going after you log off). It also supports lots of custom islands. I've had a lot of fun with it.

I love how random this mission can be. Had 7 players in the squad, just escaped the prison camp and regrouped at green mountain. I had grabbed a satchel charge from one of the guards at the start so we decide to setup an ambush near a main road. Figure we could take out a bmp or something and grab some gear for 2 squad mates with no weapons. Satchel is placed, we're spread out in a field nearby waiting for something to drive by when out of nowhere this rumbling sound is heard just behind a small hill next to us. A freaking tunguska drives over the hill and spots one of us. Let's just say that didn't end very well. We got killed trying to retrieve the satchel charge from the road :p

Just wanted to post and say great mission! It really ramps up the tension when avoiding enemy patrols, especially early on when you have little weaponry.

Monthly bandwidth limits from my ISP has made this unfeasible. Mods please delete this thread.

You could try MSO (Multi Session Operations). You can make a persistant database of your multiplayer server and it should keep everything even if you restart your machine. http://forums.bistudio.com/showthread.php?142683-Multi-Session-Operations-v4-5-released You'd need some SQL knowledge though, but the mod author is very helpful in that thread.

Just wanted to post thanking the creators of this mission pack. I've been running it a few days now on a spare computer as a dedicated host, no PDB yet as I'm unfamiliar with SQL databases. Been having tons of fun with it though, no major issues encountered yet, just the usual ArmA 2 ai driving and pathfinding skills that threaten to leave a boot print on my monitor.