For larger, more advanced builds, I think wrench events and the door mod are usefull. But in a freebuild, where everyone is either building: a car, a shack, a model of a computer, a half pipe for skis, ect. ect. All of wich are small, usualy basic builds, there is no need to make your hot dog stand shoot rockets, just like there is no need for a tank to have doors. IMO, on a free build, not many add-ons are needed, the point of a free build is to make a small to medium sided, original build. You wont have any more fun weather you have every vehicle, or 2-3. Its a free build, you just build, you dont need an ass-load of weapons, or even mods that can be usefull for building.
Just build somthing cool show it off, then either leave or build somthing else, you dont need doors, or wrench events.