Here's a guide of how to get around 900k metals and 700k oil with very low leveled units
What you will need:
- Lv3 Razorbacks
-Copter drones/Cobras (any level would do)
What to find:
A level 23 rouge base like so:
Simply destroy the bottom gun turrets with razorbacks (there are challengers on stand ground so they're not to be worried about) Be wary of the mines between both gun turrets.
Then deploy Copter drones/ Cobras to take out the storage buildings (haven't tested copter drones, they may get destroyed by the north-western gun turret or bunkers)
If needed, End Attack every time you destroy a storage to refrain from getting damaged by the left over troops.
If you don't destroy the CC, you can farm the base again when it repairs.
Hope this helps