If you dont have mods or any buddies that want to help you take don Craw the invinc, then heres and easy way.
When you enter his upper lair, youll notice him, minions, and 2 rocky objects.
Your gonna want to run tp the second rocky structer, (the one on the right, its sort of like a tunnel), and avoid enemy its at all costs. Now, your gonna want to wait for Craw to burrow under ground backwards. When he does this, make sure you have full sheild/HP. No when he flies up in the air, hitting you up as well, look down for the rock platform. Try to land on it.
Now this may take a few times, but its worth it.
Once you get up there, you can shoot all his critical locations depending on where he stands.
THe only attack he can hit you with is the spit balls, which cant knock you down, but try to avoid them.
His minions cant hit you either.
But make sure you have lots of ammo.
I brought an eridian rifle just in case. Unlimited ammo, you know?
I defeated him when i was level 54 this way.
If your still having trouble, add me and ill help. On alot. GT: Viral End.
Check my page on the borderlands wiki under NeverNegative.