Queen size cannot lay down in bed.
Wrap in waterproof tarps. Secure and strap tarps. Strap to truck from front cleat around mattress to back cleat. Then from front cleat over mattress then under then back cleat. Then back cleat over mattress then under to front cleat.
Will be a noisy drive. Check straps every stop.
Watch for rub through.
I did it on top of tonneau cover with bull rings
, top tie-down point helps.