Didn't hear scavs though as I was busy inside an agri building. All I get is "Your vehicle has been destroyed". Ruh roh.
Yes, they are quite sneaky just dropping in whenever.
I've stopped bringing any vehicle into the base, and I leave my ship 400-500m out. They don't seem to see it out there unless they've noticed me arriving (if scavs are already present when I arrive, I mean. They will aggro on your ship from quite a distance if you stay in the air too long).
Now I prefer to go in just on foot. That way, if I'm in a building, they have no way to get at me and I can see them through the windows or on my radar and prepare my exit strategy, which usually involves lots of shooting and then ducking back through the doorway(s) that they can't enter. Hehe.
It was convenient (I thought) to have the SRV close by, especially in a large base, so I could dump mats there and continue looting. But it's a scav-magnet, so I just trek back to the ship if I really need to.
I do like how Odyssey missions throw these events at you...no two missions are quite the same. It's fun I think.