I have a '95 Windstar van (lots of miles, but it just keeps going
) that we removed the middle seat from to make a large flat space for cakes. I cut an egg-crate foam mattress pad to fit the floor space and place the cakes on that. No sliding, lots of room, easy access. Plus room in the back for more 'stuff' if I need it. It has worked very well for many years. I also had a magnetic sign made that says "Patience please, Wedding Cake on board". I attach this to the back of the van when transporting. It doesn't completely stop the 'middle finger salutes' I get when driving too slow for some folks, but at least it lets reasonable folks know that I'm not just crazy!