I have a 2015 Sierra, I didn't pull the seats I just folded them up and built a platform like you mentioned. I have. two large Golden Retrievers and they have plenty of space. When we need the backseats for more people I just pull the platform and fold the seats back down. This system works great for me, its the third platform I've built for my dogs over the years. I built mine out. of 1/2" plywood covered it with 1" foam then installed outdoor carpet.They seem pretty comfortable on long trips.