That's really a question for John. I'm away from home and don't remember--does the manual call for fiberglass there? If so, then you should do it. In my own humble opinion though, if the shrouds and jib stay are properly adjusted the only force on the tabernacle comes from any bending of the mast, which is much less forceful than the moment forces you would get from an un-stayed mast. Bui I repeat, ask John Harris unless the manual calls for fiberglass on that bulkhead.
After reading about Pete McCrary's troubles with the tabernacle I did add some doubters (which John later roundly denounced) but they were to add more gluing area to the bulkhead-deck junction, not to strengthen the bulkhead. Again, though, if the shrouds and jib stay are properly adjusted the stress on the tabernacle is minimal. If, for example, a shroud breaks, no amount of strengthening will save the bulkhead. Personally I would rather have to replace the tabernacle than the mast or bulkhead.