How do you Geomerge on Sandbox in Halo 3?

[DanMan274]

Hi as you know the new halo 3 mythic map pack has recently come out and in it is the completely forgable map sandbox. I was wondering how to geomerge on it since there are no doors, especially merging into dunes. Thanks!

 

[cdoggyfizzle]

Lucky *******, I don't even have them maps yet 'cause I didn't purchase Halo Wars.