Hi Lee
Sorry for the delay in replying I have been out of the office for a couple of days. I suspect you have the ultimate one shot with the roof mount aerial.
We have tested the receiver on these at 120 meters +. As for positioning the aerial I would recommend it is fitted externally to the roof to give the best range.
The mount is supplied with a gland and you can drill a hole then use the gland to seal the hole. You could also run the cable out between the door seals which would allow the vehicle to be locked.
We are looking for a suitable mag mount, the ones we have used in test were not strong enough to hold the aerial mount while driving.
It will work mounted in the van, however you may need to leave a door or window open if you do as the radio signal may not pass through the metal panels of the vehicle.
Cheers
Ian