Hey Edwin, is that engine hoist (in your pix) for your models, too?. I use the same system you've got , making the carrier/cradle for each plane. I found PVC sched.40 is best of all the plastics, seems to have least flex.

I found out the hard way that you need to tie the tail to the carrier, somehow. I was on the way to the field one day,had my plane in back of pickup, in its cradle with the tail at the front of the bed, had done this a dozen times, no problems, and pass a trnsfer truck (on the 4-lane, 65mph) looked in my mirror to see if I was clear to move over, just in time to see my plane's tail flip up in the air and come down across the tailgate. Almost broke it in half just forward of the tail feathers. I was afraid it would blow out of the truck and get crushed by the 18-wheeler before I could pull over. So now I secure everything with mini bungies and rubber bands.

The tonneau cover sounds good, too. I got stuck at the field once when a T-storm came up. Rained for 2-hours past dark, plane too big to fit in back seat.