Go to X:20443, Y:31188 coordinates to find an easy place to keep
respawning the rocket launcher and ammunition for it. Grab the rocket
launcher in the temple. There are also five small boxes in the building
to the right of the temple. Destroy all five boxes to spawn another
rocket launcher. Then, use your grappling hook and parachute to go a
little ways away from the area (you may have to leave the island). Go
back to the area now, and the rocket launchers should have respawned.
Repeat this as many times as desired.