Loading MDF onto roof bars!

[Slime]

Hi all.
Probably a stupid question, but, my sister wants me to transport a 2440 x 1220 sheet of MDF for her tomorrow morning.
The problem is my car only has roof bars going front to back with no left to right bars.
I only have to deliver the MDF about two miles and would love to know whether there is a particular way of securing it.
I have two strong strap ties that are about 12 feet long.
How can I do this safely?
Many thanks in advance,

Slime.

 

[big-all]

you cant really do it safely without more support
the board needs support for at least the central 6ft and fully across the width
can you reduce it in size [several components ]

i made up supports from 2x1 planed [20x44mm] width off the car
then 6" at right angles inside each rail back and front each side
then carpet felt /rubber/between bar and wood and several turns off packing tape to secure
you could then use your straps across the car but you would need rope in a \/ at the back and/\ at the front to stop it sliding
the ropes would go from the back off the rail underneath to the front center off the board then back along the top to the other side at the back
the back will be the opposite

 

[Slime]

Thanks for you advice big-all.
I managed to get it done but will use your advice next time.
I appreciate your help,

Slime.

 

[big-all]

glad you managed it
with my method it cannot go anywhere so it gives you more confidence to go a bit faster