The stemhead is attached with nuts through a backing plate. It is difficult to reach through the bulkhead because it is about 18" forward and at a difficult angle. Better to put an inspection port through the deck about 6" inches behind the stemhead and effect the repair through there.
And yes you will eventually lose your mast. The bolts are slowly unscrewing over time from vibration. Sometimes the backing plate itself is threaded, so you may be able to get away with loosening the forestay while retightening the screwheads. If that does not work, then you will need to put in an inspection port. There is no foam floatation that high up and that far forward. There is actually a small void there, so you will not have to dig through much foam to get to your repair site.
I have a very poor picture of the under part of the stemhead, but the lighting is so poor that it it not very informative. If you are interested however, send my an email to
roger02@mts.net and mention this under the stemhead picture, and I will send it to you.