Speed is the key, that's why the current system works the best.
You can wait for a commander to find his seat and start deploying, waiting for an engineer to set it up. All nice ideas, really. But hey guys, this is a game where first shot happens 10 second after round starts, people don't have hours to set this stuff up like in RL.
You need to do it fast and effective in this fast gameplay. Only way to do it is like this. If you put it on a Hanomag for example, it still needs to drive the distance and try to stay alive, then have to set it up...
Too slow for a fast game. If the maps were 3-4 times bigger then it could be possible.