I was looking at the various racing seats from Summit Racing very early in my build. It was only a trade-off exercise. The racing seats I found are heavier because they have to conform to the specified crash standards for difference race organization. I also look at used car seats from the junk yards as a possible option since the custom made seats are so expensive. For the car seats, I can remove the steel chassis and leave the remaining foam and seat leather in place to save weight.
The other two options were to buy the foam blanks from Vans and do the upholtery afterward or to order the expensive custom made seats.
In the end, I ended up ordering the foam seat blanks and had a DIY upholstery using the durable and thick neoprene seat covers made for the Jeep Wranglers. They require some DIY stitching skills. My Jeep neoprene seat covers last over 10 years parking in the outdoor and they should last longer in the RV.