There are a lot of similar mods out there, but none that do things exactly how I wanted. So this is my version of modifying drifter spawns and looting.

Spawning:

• Max light level was reduced to 4.
  This makes it easier to spawn-proof underground areas.
  
  
• Spawn height was reduced to 0.9.
  From my experience, this guarantees they no longer spawn on the surface. I tried 0.95 and had quite a few pop up while exploring at night, presumably due to some shallow pits or something. I have roamed around over quite a distance on the surface at night with it set to 0.9 and haven't seen any yet.

Looting:

• Loot drops immediately, no butchering necessary.
• Corpses decay in 0.1 hours, so no cleanup necessary either.

Update for 1.20. Added all the same changes to the two new monsters.