I was thinking about something very similar. It came to me when I was viewing a preview for the TOW missile launcher by the desert OFP mod team. It would be of limited usefulness if it was just sitting there. I mean for base defense, or perhaps static at an encampment. Still you can't "take" it anywhere.
Basically what I was thinking for that. Or for anything really so long as you can change the entity name. Is to allow for a vehicle, structure, etc. With a specific name. To run a script which, when you move close to the vehicle, building, etc. Gives you an action command to deploy the gun in front of you (assuming you give a little leeway for the deploy radius around the vehicle.
The player could use the medic animation to simulate putting crap together. Then, when the gun is made. You will inversely be given an option to deconstruct it and move on to another point at your leisure. Of course adding a variable to track whether it's been deployed would be good to. Just so you can't deploy fifty million goddamned launchers around the car, because that'd just be gay. =P
I hope someone capable and ambitious enough reads this. I'd do it myself. However apparently I have a brain similar to that of a monkey addicted to huffing gasoline. So, eh.