If you want to mix things up a bit, look for Planetary scan missions which offer MEF as a reward and then go and do them in a ship, rather than using the SRV.
Most of the planetary bases that are your destinations for these missions will also have the data-point "caravans" (usually 3 or 4) which you can scan first to get extra Encoded mat's, then you'll get another wad of Encoded mat's from scanning the mission-target terminal and then you'll get paid in MEF too.
To be clear, look for missions that specify low/medium/high security outposts.
These are the missions that take you to permanent bases, rather than the bases that pop up after you hunt around a search zone.
Long as you're not already Hostile to the faction, the base won't start shooting at you while you fly around, scanning the caravans.
It will start shooting when you scan the mission target but you can just boost outta there and head straight up into orbit.
Honestly, farming the Jameson site and then trading for mat's you need is probably more efficient but, lordy, it's dull!