I'm stamping the maps together (which by the way, I have just done. Operation Lynderdam is underway!), but it can cause some massive issues, as all maps are based at different heights, so you have to prepare the ground where you are about to stamp by adding or removing height based on the existing map stamp. Basically, a pain in the arse. But when it works, it looks great!
And you'll find that everyone's stamp tool is broken, unfortunately. I think it was on Relic's to-do list, but never got fixed. Fortunately there was a pipeline.ini made that you can add to the COH directory that fixes it, but I can't remember for the life of me who made it. Credit where credit is due, but my memory is atrocious!