If you are far enough away not to hear the shutter opening and closing then that could be problematic with a standard bulb.
An idea would be to adapt the bulb from a blood pressure cuff for the purpose. The bulb can be locked after squeezing via the screw valve that is part of it. When the time period is done then open the valve to complete the exposure.
This, of course, depends on an air tight connection to all components. Otherwise leak down will cause a failure to remain open for the indicated exposure.
The mirror slap issue with long exposures is negligible. During the last full moon I made landscape exposures using a SRT 101b with and without MLU. There was no noticeable difference. All negatives were sharp with an 8X loupe.