I've been looking at getting my disco 2 under sealed but Iam confused which is the best as I have seen a lot of surface rust round the rear chassis frame and as I tow a large caravan I want it done properly also the body of the car is immaculate. I would be grateful for any advice or recommendations

Welcome. Take this to the discovery part of the forum and you'll get advice. That area of the vehicle is prone to rust. Should be monitored closely otherwise it'll be terminal for the vehicle.