Pretty sure I'd still just run him raw. Any points you put on biggs are pretty much wasted since he will literally die first every time unless something crazy happens.
If you put R2F2 on Biggs, you need to put on Experimental Interface. Makes him expensive, but it's a solid build. No IA on him, but more survivable this way.
It's not survivable enough to justify spending 31 points on him. That's no longer in "throw-away meatshield" territory, that's in "centerpiece of my list" territory. Better to invest in the guy Biggs is protecting so he can make the most of that protection while it lasts.
Biggs will die so there's no point in piling on upgrades, IA and a cheap mech is all you should give him.
All of this. You run Biggs so it takes 10 hit points (12 with IAs) to kill Wedge or Luke. I see so many builds where people are using Garvin or Cracken or Katarn to give Biggs extra tokens but you have to ask, "Are they there to protect Biggs or is it the other way around?"
Best bet is R2 or R5 with IA for 26 points. If you have a point to spare, then maybe R2-D6 and a discard EPT like Crackshot.