I can't figure out how to geomerge on any maps other than foundry because none of the other maps have Doors. How do you geomerge on Sandbox and other maps like Avalanche, Blackout, Ghost Town, standoff, Rats nest and other maps with immovable objects?
There are many methods to do it, but you should check out the most recently discovered way: New Forge Glitch
http://www.forgehub.com/forum/halo-forge-discussion/85018-forging-101-merging-sandbox.html My tutorial.