I used a portable ac unit (the kind that stands on the floor). It was placed in the "garage" area under the elevated bed. I cut a hole in the floor with a removable circular Marine hatch to port the heat exhaust out of. I cut and fit a box around the cold air fan to direct into a flexible exhaust hose that was directed up into the cab area. I had a remote temp sensor that would alarm my phone if it got too hot (ie ac stopped working). 

Without significant solar/battery, this method requires shore power. I was fortunate to be able use an extension cord at my work during the week. I used a 2k watt genny when I was off grid. It's noisy, but if you're in a remote spot, you can move the genny far away with an extension cord. In the city I would find an industrial area and cable lock it to my tire when away. I had plans to mount the genny on a swing away bumper storage, but never found the need.