ER70 dash 2 or dash 6 is the silicon level in the filler, more silicon is used for MIG welding because it's a dirtier process. Either TIG or MIG should be on clean bright metal, no mill scale , no oil or grease. But TIG really needs it.

Chassis work with a 110v TIG is probably reasonable, assuming you're not going to be welding .120 wall DOM or similar. .083 wall 4130 should be doable with 100A output or so, which is no problem on 110/115v current with a 20A breaker, possibly even on a 15A breaker. 110v MIG is best for sheet metal or skillful and experienced welders, running joints vertical uphill, preheated and/or beveled. S/F....Ken M