Regarding 18.5" 12 V TV. Is this suitable to be affixed to a flat shelf. Is there holes etc to screw/attach base to shelf.

The TV's do come with various desk stands, however they are not designed to be screwed into and hold while the vehicle or vessel is moving.

We suggest to pack the TV away if you need to use the Desk Stand, or purchase a wall mount with locking pin to secure the TV.