The 5 series aerials are really good as you can turn them to get the best signal , but you need the room inside the van to accomodate the aerial pole, so you need, preferably,the pole to come into the wardrobe or with some you can get shorter pole to fit inside a cupboard.
http://www.visionplus.co.uk/shop/the-new-status-580-directional-tv-radio-antenna-system.html
Location will depend on where your current aerial is and whether you can utilise the current hole through the roof, enlarging it to accommodate the new pole, or whether you need to cut a new one.
When removing the old aerial you can get a blanking plate to cover the original hole and screw locations, use a good bead of soudall fixall to seal the blanking plate to the roof.