For your convenience, the text of the post once again:
While this might take longer than the raid-finished-base-with-G9-Eclipse-one, this doesn't need any sophisticated timing or other skills.
Might not work on all platforms - I can only test on PS3.
Description: There is another respawnig Propaganda Trailer in Bandar Kayu Manis during the race "The slopes of Gunung Kudus". The village had been 100% finished, so there was no Propaganda Trailer anymore and the race had already been beaten before. Now start the race and imidiately restart (or later - it's up to you) it. You will hear the familiar sound of the Panau national anthem. The trailer is guarded and destroying it rewards you with 1000 Chaos points, $5000 and apparently some 0.xx% towards completion.
How to exploit: After starting and restarting the race, destroy the Propaganda Trailer with your explosives. You can kill one of the tougher guards to get one frag grenade back from his loot. Don't care about health, it's restored when restarting the next race. Leave the area in the deployed red Maddox FVA 45, e.g. by driving over the edge of the cliff behind the big "fortress" building to be out of sight and lose heat and to also get out of the mission area of the race, arguably the fastest way to end the race. Climb back up and repeat.
Please TEST & CONFIRM: I haven't finished JC2, yet. I'm not even in Mercenary Mode, just having done a mere 45% of the game, but I was able to raise it to 46% (as seen in the save game info) by only destroying said Propaganda Trailer about 10x (never finished the race a 2nd time). Found this by accident, when I crashed the red Maddox FVA 45 during the race.