Reddit reviews Gorilla Heavy Duty Ultimate Construction Adhesive, 9 ounce Cartridge, White, (Pack of 1)

I have not gotten there just yet and luckily my roof is metal, so I was able to attach framing with rivnuts-- but if you are faced with this and you have fiberglass ceiling, I would install furring strips (1x2 or 2x2) using a Gorilla Glue construction adhesive like this one https://www.amazon.com/Gorilla-8008002-Ultimate-Construction-Adhesive/dp/B07MMF7FHD/ref=sr_1_4?crid=27S4836F586LD&keywords=gorilla+glue+construction+adhesive&qid=1571854698&sprefix=gorilla+glue+construc%2Caps%2C165&sr=8-4 (did some research, apparently this cures faster than locktite and holds better).The strips would be your framing. Then you can install whatever ceiling material you want (e.g. ship lap, tongue and groove) you want and secure it to the framing :)

Edit: I am not a pro - but I have seen others here do this so I think it should work fine. I would recommend swinging by the subreddit again on the 25th during the pro van builders AMA and ask them just to see what they recommend. Measure 2x, cut 1x ;)