A friend of mine used two old wooden pallets, set the pots on them, marked them. Then used a jigsaw to cut out the circles. The pots set down in the holes about five or six inches. If i remember he could haul about eight large potted plants in a standard pickup..

1. Put a topper on it, tie the plant down?

or

2. Loan your pickup to someone who owns a van, borrow his van?

or

3. Pick a very calm day, tie the plant down, and drive 3mph to your destination?

lay plants down in bed truck get tarp size bed or smallest you buy. Buy one box of 30 zip lock bags the kind don't have slider get pop type fill with dirt sand rocks add to top tarp hold down.

I got some trees at attwoods couple of years ago. 3 bradford pears and two bald cypress. I put them up in the truck upright, got up into the truck and laid them down root at the front laid all the rest and let the trunks lie on the tailgate. I had 30 miles to go, I drove 45 to 55 MPH and didn't hurt them a bit. I think it was from: laying down and bunch togather. Standing up you will only be about to go about 20 MPH if that, it will either blow them over or start ripping the leaves off from the wind over the hood and cab. Seems to be and air pocket laying down in the bed. Worked in my case. I tried to say below 45 MPH but that was hard.