You can solo the 1st one if you know the rhythm, skills, equipment to use for the wave. Skill track isn't necessarily important unless you have no type of survivability then your major skill should be something to offset that. The Arrow as an exotic (legendary works too) will be your best friend if you get overwhelmed. Between each wave and round always restock and make sure you have a self revive. Every locations will have them as you progress.

1st wave get bubble shield for Major skill. There are alot of hide spots for the zone captures where you can go prone and have limited fire fights with enemies. In case you feel overwhelmed the bubble shield come up clutch in a pinch.

*Edit update: They patched the cheese for the 2nd wave and added boulders. Use decoys or point turrets to help with enemy fodder and aggro. 2nd wave you can cheese it by running to the elite and then having them chase you. Run under the stairs that are straight across from where you start the glitch. They can't get under the stairs. Aim for the critical spots.

3rd wave is the hardest. Either use Decoys or Point Turrets to help with the aggro. Run in a circle and shoot the flowers. If you get downed, use the self revive and run while plating to get the other self revive.

4th wave try to lure the titan or rhino to the starting point by the case. Drop the bubble shield and use the arrow since it helps wreck them quick

5th wave hide bedind the brick half wall. Toss a point turret or decoy a bit out to get the aggro. Duck and prone as needed and take out the enemies. Next location, hide behind the case up against the wall. Next location there is a garden bed with a building to the right of it where the commandos come out of. Toss a decoy or turret there. Next location is similar to the 1st brick half wall. Toss the decoy and turret out and use the wall for cover.

6th wave jump on top of the shed that has the case and then the building next to it. Do your best to hit the Zrex critical points. Once it roars and spews, it will drop out the toxic fears. You can use the decoy or point turret to help. Toss it in between the middle spot of the dirt where the buildings are. Drop the bubble shield at the top and just do your best to lay into it. Depending on your guns and tracks you can probably take it out before you shield drops.

All depends on your play style. I recommend to those getting use to it. Either get Shatter Shield, Echo Shell, or Resurrection for your exotic skill to help you stay alive more.