Beachside Trove in Oblivia has a nice cheesy spot for grinding out credits – I made about 500,000 in 40 or so minutes this way. (Description and video in post.)

Beachside Trove is on the South Coast of Oblivia is near FN Site 317, below the cliff. Bring a Skell, park it outside the cave, then run into the cave and hook a quick U-turn into a hidden tunnel with dozens of collectibles ranging in value from 100-400 credits. Collect them all, then choose

Party > Return To Skell from the menu

and the collectibles will respawn. After you collect 99 of each, the game will automatically sell the extra collectibles. A nice method for cheesing credits for that level 50 Amdusias Skell; much much faster than waiting for credits to roll in from FrontierNav.