Just an update, in the latest development build most of the on-load errors have gone away, only one remains: vehicle part laser_guns has the TURRET flag, but is not made of a gun item
Errors in the part install menu persist for laser turrets.
Blaze, which parts are blocking installation of mountable guns? I had visions of installing a mountable hypervelocity driver on top of my driver seat but no dice it seems. Also, it doesn’t require a turret chassis to be installed first (contrary to the description)?