Hey woogawelder,

I did just what you are planning to do and I don't reccommend it. It's not just a matter of finding work but also you're fresh out of school and don't have the experience. It's one thing to do stringer beads all day in a flat position on a nice welding table in a nice shop, but that's never what needs to be welded on! Not to say you're not good or anything (i haven't seen your work so I don't know) but there's so much more to welding than laying down stringer beads all day. You really should get some experience in a shop first before you go out on your own. You need to learn the way things are really done and all the tricks that can save you out in the field. A big part of mobile welding is repair and repair takes a lot of weld preperation (grinding, sanding, air arc gouging, etc.). Also, you will find so many costs and things you need to buy that you never anticipated (consumables, gases, tools, welding blankets, etc, etc, etc...).
I would reccommend you start out slow and get the word out. Don't expect advertising to work instantly; word of mouth is much better. Make up some nice business cards and hand them out to people. I sent out a "flyer" to about 10 different vineyards in the area with my business card mounted on a magnet in the envelope. A couple months later, one of those vineyards called me because they kept the card on the fridge. After I did the job for them, they reccommended me to another vineyard who has continually kept coming back to me with work. Bottom line, If you do good work, people will come back to you and the word will get around.
As far as truck vs. trailer, get at least a 3/4 ton truck and mount the welder in the back. Then use this truck for your daily driving, people will see you welder (especially the Miller blue ) and ask you about welding. I've got jobs before from just driving around town!
Anyways, I could probably go on forever so, good luck! I hope you are very successful...Oh and one more thing, never get discouraged !