As i'm Lt. Colonel, i always use the Close Protection gametype that gives me 12 points to build my squad, helped by having an officer thanks to the Wespoint ribbon.
So i got immediately 3 machinegunner that i sent to roughly the middle of the screen.
Once 4 points reached, bought an engineer and once 5 points, built the bunker with the 3 machinegunner inside.
Then after 2 points, built a trench in the bunker to help the machinegunner.
After that, 5 points waiting and built a camo net on the bottom right of the screen.
Started then to wait and buy bazooka soldiers each new 4 points.
Each time i had 2 bazooka in a camo net, i built a mortar pit for them, then moved to build another camo net and continnue the process.
Luck is very needed and i had plenty in this game as lot of crates fell near my MG troops (and getting the crates with the MG guys gave them experience more quickly than simply waiting for them to kill, gave additional points and even lowered the amount of attackers)
The MG are plain awesome once they get a few ranks, and 3 ranked MG in a bunker are simply killing machines, they were a big reason of why i could last that long.
Sometime a lucky enemy strike destroyed a camo net, i had to rebuild, and thanks to the numerous bazookas i managed to hold against tons of vehicles and some blitz waves.
Can't even imagine how it would have even be possible past wave 100 without that much bazookas (i read that they don't fire anymore in current non-downloadable version ! good i wasn't playing it with 2.2.7 then, would never have made it past wave 100).
Unfortunately in the end i was losing more troops than i was gaining points to rebuild.
At the peak of my perimeter defense here was what it looked like :
At wave 190, when all was going to be lost :
Debriefing :
got a few ribbons from that specific game.
Good that it's possible to pause the game with the space key, it was way too long for me to deal with in only one sitting, but i think it would be nice to be able to save a non-yet completed game, as it can take a long time.