LazyK beat me to the punch. I mentioned a cabinet blaster earlier, well the shop also had a large, walking, your suit up to blast cabinet. You could fit a Beetle in one. We experimented with various media to blast fiberglass. Some sort of plastic looking pellets. It worked, but was tedious to do. The method we normally used to strip paint off of fiberglass was paint stripper. It worked, but was fairly nasty stuff.
Soda blasting is supposed to be gentler, but I hae zero experience with that. No idea how quick/slow it may be, how long thee media is useable, etc. HOWEVER, and this is very important, if you have an oil pan with baffles anything else will be a big no no. Soda blasting residue can be easily washed away. Sand/garnet/slag etc will leave a residue that is hard to clean and will destroy your engine if you do not get it all out.