Here is my solution as I too noticed movement at certain "speeds" say no more...
....I used Pauls idea of the luggage strap bolted to the inside of the rear storage compartment which will hold down the hood and took it a step further. I made two small angled brackets from aluminium and attached some strap to them. These brackets then simply hook into the rear deck section - see photo- there is a very handy gap for the bracket to fit into...the straps then drop straight into the storage compartment and attach to the luggage strap. U can get some good tension on these and no movement in the deck at all....and they can be easily undone plus u don't see them, or they can easily and quickly be removed completely... simples..
