Creating a Stranded map

I had to create this thread because I'm curious, since Mr. Crow Guy claims he knows which pieces are needed into the creation of a Stranded map, about a possible guide or any source of information that will help assist me in attempting to create a map like this?

I've used Hammer Editor for quite some time (re-created my house and worked mostly on Alien Swarm maps) and I have a pretty good idea of what goes where, but (without searching google, since i'm lazy and it's easier getting direct information from someone who knows) what is needed to create a Stranded map?

Stranded maps all they need is landscape and water.

I'm pretty sure Tree and rock generation is automatic.

I got a hold of the creator.

Apparently all CS:S and HL2 episode tree's/rocks work. That's good news. I'm on my way to creating a map then...

<3