Lately I've been taking down entire AOs by creating a FOB with only situation room, medical tent (might try it without this), and checkpoint, making sure it is located outside the AO. Transport 5 large supplies in with one ammo crate, and that gives you approx 18 hours. The next step is to use a little bird to set up check points around the AO that last perhaps 2-3 hours, these enable you to spawn in quickly if you get hammered and saves a lot of walking. Once I'm inside the red zones, I switch to RTO and call in air strikes once I get visuals on AA, or HQ targets. So I use a basic rule, if I cannot see a target I dont use the RTO, if its dark I sneak up on an AA or artillery point blank and plant charges. Another technique is to when you go down close to a target hit D and you can crawl closer, set off charges you didn't get a chance to detonate or even call in an air strike on top of you!