Pretty simple idea here... pack as much durability as I can. I have 4 points... what do I add?

Just take 3 Defender instead

Swap for Vessery with TIE/D, TIE/D, VI, and give all your Defenders TIE mk.II. Vessery hits, lowers evasion on enemy ships, the Deltas focus fire the same ship. Should be brutal.

I love the baseline archetype of two /x7 Deltas and a 3rd ship. Deci might not be my favorite third ship (Phantom, Silencer, 3rd Defender all come to mind, maybe even Upsilon), but I think it might be wise to go Oicunn. That'll leave 2 points. I'd say Intimidation or Ion Projectors (and Adaptability or Trick Shot).

I don't think there's anything you could add for 4 points which would be better than the pilot ability and Elite slot. Imperials don't have great dice-mods crew like K4 or Dengar (Kallus doesn't cut it in my mind), you can't fit Gunner, Vader doesn't seem worthwhile in today's meta, and Kylo seems weak if you're just hoping for lucky crits. Maybe Rebel Captive would work, to either mess up your opponent if they focus the Deci first, or else it could be a fairly strong endgame piece if you're able to bring things to a 1 on 1. I think I'd rather have Oicunn ram damage, however. A Patrol Leader just isn't going to do much damage, and you do need to kill stuff eventually.

Since your theme is durability, moff jerjerod. Than throw on intel agent and inspiring recruit. Use them as is, than eject them out the hatch with the moff to get rid of some crits. When the courier droid comes out, you could have a 0 point card to eject. That negates 3 crits a game total. Especially direct damage, weapons failure, Etc. Could make a big difference for 4 points