What I do is to place the shepherds pole and bar down on the mattress and then fold over the mattress so both the pole and bar are sandwiched between the folded mattress.
Then I go outside and push as much of the canvas as I can onto the mattress. Last, I'll push the end closed while also stuffing in any extra fabric so as not to pinch it in the seals.
DW, 3 Kids and our Goldens
2012 Shamrock 233S
2008 Toyota Sequoia 5.7L 4WD