If ya wanna build it cheap, heres is one of my old plans e,f or g...
Go to the local rv dealership, figure out your cab to axle length and how much you'd weld on the rear of the frame to help relieve the front axle balance.
Then find a used class C (or even an A if ya cut the cab section off) motorhome with engine trouble or a nice pull type camper remove the camper or box off the frame of the original unit and set it on your truck, with some big tool boxes under the body, then re sheet or re-paint every thing to match, and you are good to go.
I'm thinking a big class B box would be a pretty close fit if you simply cut the overcab section off. The pricing on those class b's older models with litle or no use over the last 10-15 years is almost free after you sell the cab / chassis after the removal of the camper box.
Some of these can look really good, others really back woods redneck. Not that there is anything wrong with either, I'm sure even the crudest design could be fun to party in.
-blizz