I recently bought a used Synlawn putting green that's ~12x14 feet and plan to install it in my backyard. I've figured out the logistics on how to get this massive, heavy-as-hell carpet from Point A to Point B, but I am not sure what sort of base I should have for it.

I want the green to be relatively flat, but I'd also like to work in some contour at some point by shaping either the material underneath or pulling it back and adding some shims of some kind or another.

I've been reading a lot on this and see all sorts of advice for DIY synthetic putting greens. Some say you should place it over builder sand, others say use crushed gravel that's flattened down...some even suggest putting it on a rubber or weather treated wooden base or some other firm surface.

Any ideas or advice?