Ready welder
 

Not an actual mod but a great product that works as advertised. also costs less that an onboard welder.
I have one of these, the basic 10000 model. They work great. I actually bought it to use as a spool gun for doing aluminum. using the Argon gas setup I already own I was able to weld a 3/8" aluminum plate onto the bottom of my boat's stern drive after the arm that holds the stern drive up fell of and I ground about 3 inches of the bottom of the skag off before I realized what happened. all u need is 2 standard 12v car batteries (you don't need fancy deep cycle batteries) and you are up and welding. :welder:
It also welds with solid core with gas and gasless flux core on steel.
ReadyWelder:welder:

That looks awesome!

How does the wire feed spool work? Where does it go? Is there a carriage for it or does it just sort of lie there? Also, how long do the batteries last before recharging?

it uses 2lb standard spools of wire . they go in the bottom of the handle there is a spindle and tensioner for the spools there, and the wire drive is right up by the nozzle so its pulls rather than pushes the wire. I also have a mig welder but if you know about welding aluminum, the wire is so soft that it doesn't feed well when its pushed thru 10 feet of cable to the gun and jams up easily... no a problem with steel wire. its already setup for gas too you just need the tank and regulator if you want to MIG weld with it. nice thing is that you have a fingertip speed control and its 100% duty cycle. I have only ran for about 20 minutes on a couple of old spare batteries i have laying around but didn't run them down... I think they say about 45 mins to 2 hrs of welding on an average set of batteries.
Oh and I got it used via ebay for about $200