I know it's me, how do I toughen up Cap?

I'm struggling to do some of the endgame stuff and am dying far more than I think I should be. Looking for advice as to how to toughen him up a bit.
My artifacts are: White Gorilla, Gem of K, Taskmaster's, Sabertooth's.
I've got a Kurse Medallion, +800 def with Power Doop Uru.
My legendary is Savage Axe.
My ring is a IC Signet
Slot 1: Fragment
Slot 2: White Gorilla
Slot 3: Caps
Slot 4: Caps
Slot 5: Caps

I know one area I need to improve is finding an inv core.

So any pointers on what I should work on to make him a bit more tough in CDR or even the cosmic areas would be really appreciated.

Thanks!