Tie one end of the rope on a handle on the rear inside roof of the car.
How to tie a mattress to roof racks.
What types of tie downs work best.
Be sure to crisscross the rope over and under the mattress and roof to secure the mattress to the car.
Center the mattress in the middle and put the rope over the length of the mattress.
If you do secure your mattress to a roof rack or safely in the bed of a truck strap it down with ratcheting straps.
Pull the rope tight so there is no extra slack.
Once tightly packed in the mattress bag haul the mattress onto your roof and center it in the middle.
Ratcheting straps are much less likely to fail when moving a bulky item like a mattress.
Mattresses are large bulky and can pick up resistance from the wind.
Roll down all windows.
If you do put it on the roof of your vehicle have a strap run from front to back as well as from side to side.
Use a tie down that wraps around the item and the rails.
The mattress had lifted up in the front and ripped the roof racks right off.
Use strong rope or straps and make sure the mattress is tied down lengthwise and widthwise keeping the fastenings well centered.
Tie the rope that you placed the mattress on in place.
With the third option crossbars with side rails you can secure an item to the side rails and run tie downs from front to back securing them to the crossbars.
Put a piece of rope on the roof of the car that goes from back bumper to front bumper.
Drive on surface streets if possible to avoid heavy air pushing up on the mattress at the front of the car.
I came across a guy on the highway that only had a strap going across.
First wrap the mattress in a bag new mattresses generally come in one or you can buy one at a hardware store and use packing tape to close the bag and secure any loose plastic.
Then place the rope across the mattress length wise then secure both ends starting with the front then the back to the front and back bumpers respectively.
This will stress any knot no matter how securely tied.
Put the mattress on top of the car and rope so that it goes length wise with the length of the car see pics above.