Replacing Bed wood concerns/advice.

[custom10nut]

I’m about to start taking. My old bed wood to replace it with the new.
Of course I have to remove the bed, In order to paint the back of the cab, and front of the bed.
Considering to weight of the wood, is it better to install the wood, with the bed mounted?
Or put it together off the frame, and then mount it?
I’ve got the ability to lift it on and off, but my issue is hands. I only have me and my neighbor.
My fear s getting it ready to mount back on, then it be too heavy and unwieldy to control, and end up scratching my new paint.
Sorry for the ramble, but sometimes the mind starts to race.