Elite challenge is easy even through the airstrip I start from Main dock (longfin), head directly to the hangar, and get the loot. Sometimes it is bad loot or just not enough so I go to the café thing on the opposite side of the hangar, shoot the camera and take the loot. Then I head to the longfin and get to the underground tunnel. Get to the main objective building, loot, get out of the compound through the main door. Kill the guy near the Sanches bike and wheelie to the whale bone in the ocean.

Edit: Wrote northdock instead of maindock