October 2019
stationary should be repairable, just like normal vehicle. Right now the support class can't repair a stationary weapon even when it shows a repair icon above it. No, DICE didn't intended to let us blow up a stationary then to rebuild just to repair it. Repairing should be avalaible and is now bugged. Even if you play support and you choose the repair tool the hamer change in a wrench when you are close to the stationary and that means that you suppose to repair it. Destroying is not repairing just to clearify.
October 2019
where did you get that idea from, DICE never intended to this feature where you destroy something to repair it. It is bugged!
October 2019
Bugged or not, would be good to bring it in as new feature then.
You can repair the canons hitched by cars , but the one build as fortification only when destroyed. - rebuild