Yeah, I see what you mean. I don't think I'll worry overly much about the bridge after all- if it goes, the mission fails, but I don't want to make the bridge unrealistically frail, either.
The mission is quite fun. I've set it up late at night with a fair bit of fog, and watching the BMPs cross the water in their amphibious mode once the bridge gets blocked is really cool. If I'm really thrilled with it, I'll put it in the beta testing forum, but it's not that great really.