Series 1 Land Rover antenna

[pdes]

Hi,

I am installing my antenna on the rear draw bar (which is a huge lump of metal bolted to the chassis at tow-ball level). I am not expecting to get great distance with this as I just need it for green laning etc. However, I an not able to get any SWR reading below 3. The vehicle is a canvas topped truck with a tail board. When the board is up, the whip is adjacent to it for about 1/3 of its length but the top 2/3 is above the vehicle's waist line and adjacent to the canvas.

Given the above and that the vehicle pannels are aluminium, would this setup prevent me from getting an acceptable SWR?

Thanks

David