The watertightness is ensured by a cover which presses the cable(s) against a rubber seal whose shape prevents water from penetrating. The whole unit remains watertight even without cables.
The product incorporates two female USB connectors (1 USB-A and 1 USB-C), each of which can deliver a maximum current of 3 amps: it is therefore possible to charge two iPads simultaneously.
The mounting is done in a bulkhead, with a standard size barrel (30mm hole - max. thickness 25mm) held by a lock nut. An additional screw compresses a seal at this point, and prevents the plug from rotating.
Caution : no wiring cable is supplied, you will have to do the wiring yourself on the 12/24V network, preferably with a fuse protection.