most successful "sponser getters" i've heard of have a real vision for the use of their vehicle...
consider the events/places that a sponser will have its name seen at...
consider the time commitment that might be required of the "sponsoree"
other than that, its basically a matter of asking enough people, that out of the 100-200 companies you ask...maybe 4 or 5 will say yes.
also, look to small, new companies who are needing exposure. it would be worth it to them to give you a sample product(roof tent, rack, tires, etc) and some stickers/emblems, to simply get the word out.
then, take QUALITY pictures of yourself/your rig at said event....TDS, Jeep jamboree, etc. for their marketing department.
also, consider products that might not be that exciting (cupholders, storage containers, lights, etc.) first, cuz a company that see's a vehicle that is already sponsered by a few companies, might just get on board due to the fact that others have seen the benefit in sponsoring you. This could be your ticket to other high dollar (tires, suspension, refridgeration, comm. systems, tents, racks,etc) sponsers.
heck, i'd even consider asking a fuel/lube oil company. if you used their products specifically, advertised on your truck, and they could put you in an ad. saying that you used such and such fuel/oil/additive/etc. to "go around the world" or "to the end of the world" or something...it would be great PR for them and a endless gas card for you.
regards,
brian j.