My very first employment as a treeguy was almost identical. Bossman provided me a flatbed and said, "Go get em." He sent me out alone.
I learned very quickly to relief-cut where there's a major fork so that the limb will collapse more linearly. And not to stack the brush on the truck one stick at a time. Relief cut and stack wherever the drop zone is, into a huggable pile not too heavy that you can't carry. Stomp on it to compress as best you can. From there, drag, or hug-carry or get er up on your shoulder, the key being tight, linear bundles.
An additional trick that served me well was to put two wrist-diameter straight (or slightly curved) sticks across the middle of the bed of the truck, spaced about shoulder width. They should be long enough to <i>just</i> overhang both sides of the bed. Then lay a strap with (ideally) a cam buckle across the bed, right between the crossmembers. Now, you're ready to load.
Some of your 'bundles' should face cut-ends forward, some should be loaded cut-ends facing back. This keeps your load balanced. Don't dice branches and limbs into shorts; keep them as long as possible.
Once you think you have a full load, flip the strap over the pile and attach to the locking cam. Take the tail of the strap, get up on top of the pile. Pull UP on the strap as you jump up and DOWN on the pile, tensioning that sucker as best you can. You'll find you only have a half to 2/3 of the load you thought you had.
The cross-members are for offing the huge heap. Step between them, deep knee bend, grab, lift with your legs, the entire pile will roll off the side (if you've removed the stakes). Jump off, retrieve your cam strap and you're outta there.
You have a very simple system. The beauty of that is low overhead cost, low maintenence, small storage site (your driveway) low insurance on equipment, meaning your profit margin can be higher on a per job basis if you do it right. I did your system for a year, then upgraded to a beefed-up small utility trailer for another <i>four years</i>. Currently I have a simple system, still based on a flatbed pickup, but I have a killer bomb little 6" chipper, making my job easier, but with that comes increased overhead and operating expenses. My daily takehome, interestingly, is very much the same as when i was stacking brush. Now work on your aerial talents and customer service. Get liability insurance as soon as you can. Clients will tend to not ask the big guys for certifcates because it's almost assumed they have insurance. With your rig, its almost assumed you <i>don't</i>. Get insurance, carry it with you, cross that threshold and play the game. I'ts not how pretty you are; it's ultimately about how well you care for the trees. Keep that focus, and good luck.
