I've built the majority of my jeep with a 110 miller160, It's an older 110 welder but works the balls. I also have a 220mig and water cooled tig but those are at my fathers house and when the jeep is not movable, I use the 110 at my house.
If you know how to prep metal, and how to propperly weld, you can weld 1/4 with out issue. 110 welders get a bad wrap because it is pretty much all that the average garage build guy with no welding experience can afford, then they pollute their vehicle with substandard welds, they break apart and he ends up blaming his crappy 110 welder. Common newbie issues I often see:
-Using .023 wire to weld 3/16 or thicker
-Not cleaning the welding field
-Having a 110 welder plugged into a 15 amp outlet
-too quick of a wire speed or too quick of a pass
-Using an extension cord that is not properly rated
-Using 95%-5% CO-Argon gas
There are other issues, but these are teh most common I've seen cause bad welds.
My suggestions.
-14 guage or thicker I always use .030 minimum, .035 for 1/4 and thicker
-I only run 75%-25% CO2-Argon with a 110 welder, the increase in shielding gas allows for hotter burn, deeper penetration.
-Always plug a 110 welder into a 20 amp outlet. if you need an extension cord, get one that is properly rated. RV stores will sell a 110v 50 amp rated cord with regular 110 plug ends for RV generators and camp plug in and stuff.
- Prep the surface, remove any debris that will contaminate your welding field or not allow for a good arch. people don't realize that metal is shipped with a coating to prevent rust when in storage, that needs to be removed. I like to go a step further and lightly grind before welding joints.
-Go Slow
Lastly I highly suggest not getting a harbor freight welder... you will get exactly what you pay for.. a crappy cheap welder, the internal components are just pure crap. Hobart makes a handler 140 welder that is a very good entry level welder, it will be more of an investment, but will last you far longer than some imported japanese POS.