As far as I know there are two ways to approach the seating issue. One is to use a seat that sits on runners on the floor direct and has a frame. The other is a light weight seat that clips in and out as in some original cars. For these latter type of seats (and I haven't seen many of these in use over here yet) the way Brian Pepper used to make them was in nylon with the brass rings with a light plywood back and base that then had either a velcro or twist studs to grip or clip on the cockpit tub. Most people however use a seat that has an integral frame. The standard GTD items used a steel frame and most opted for the leather covering with brass rings. As a further option they used to offer a high sided seat if you were skinny and slid about on a normal seat (like I did!) Seast runners allow for different length drivers. Frank Catt now produces or knows someone who produces for him a seat that more closely resemble the original style of layout but with an integral frame made from aluminium, therefore saving some weight. His seats also incorporate a centre section for covering what was originally water pipes (I think) but for most now is the handbrake position. His seats are comfortable and can be made to suit quirky posteriors as required!!! Some people then put in an adjustable lumbar support as made by Sparco which can be pumped up or down to suit the individual. the only other alternative I know of is to use a foam seat made in the style of single seaters and moulded to the driver. One required per driver. Then, like the clip in seats aforementioned, the harness hold both driver and seat into place.
Just don't do what James Hunt did on preparing his for first ever race as he had a deck chair in the car and so failed scrutineering.
Malcolm
