Damn heat reflective windscreen!!

I've bought an Advent GPS 400 for my husband's birthday next week as a surprise but someone has just informed me that the heat reflective windscreen on my car (Citroen Picasso) will seriously affect the use of it. Does anyone know how to get hold of an external antenna to fit the Advent?

I have a Xsara Estate, heat reflective screen, and although the signal is weaker in the car than outside, try positioning it on the far left or right near the side window. Also stand, or hold unit, outside car to get lock before positioning inside. Some units work better than others behind a reflective windsceen, yours could well be one of them. Good luck and Happy Birthday hubs.

I should add, with first use it can take some time to get first lock on satellites, so stand outside under an unobstructed sky, 10-15-20 minutes or longer could pass Just be patient. Again, if not used for several days the lock will take longer.

Thanks for your help Border Collie - Standing outside the car with it before using it works a treat!!