3d prints have microscopic holes inside, it’s porous. I wouldn’t trust it depending on the application. You can seal the outside and they also sell additives to lessen the effect (here’s a video about it: m.youtube.com/watch?v=Q8x-mjjT8j4) but casting resin might be better (haven’t tried).

Fiberglass if the object isnt complicated to make would be the best option. Bending and cutting pvc sheets is also an option. Soldering pvc and rolling fiberglass isn’t really difficult but they both require specialized tools/materials.