Re: Flux-core/MIG for frame welding?
Most new welders move far too fast when learning to MIG weld. Cut that wire speed and slow down to get good penetration! With proper chamfering on thick stock you can easily get perfect keyhole penetration with even a cheap mig. Same with stick. Most people try to move far too fast with small buzzbox welders. The key is to turn it up, slow it down and watch the puddle, not the slag.
If more is better, then too much is just enough.
If you can't afford it, build it yourself.