[Liberate the camp bounty]

Yeah this needs to be addressed. I never had this problem until Fortuna came out. It pigeonholes you into using Mesa or some other nuke frame on the plains if you want to finish this particular stage.

[Recommended SOLO frames in Orb Vallis]

I mostly use Mag for the highest level bounties in both Cetus and Fortuna.

Quick Thinking, (Prime) Flow, Energy Siphon, and Energizing Dash pretty much makes you incredibly tanky. Use Magus Elevate to prevent stunlock whenever your shields get broken. Also, roll a lot! It gives a 75% damage reduction throughout the animation and it helps Mag (and other squishy frames) in survivability. 

[Which frame is your fav/your main frame]

Mag! Mostly because she was my starting frame and the sentimental value is there.

As far as weapons go, Boar Prime is my go to these days.