It's possible to do, but as mentioned above, I would only do it with aquarium safe silicone. I made PVC tunnels/caves just as you mentioned, using aquarium silicone. They held well. Silicone is better to use, since you can take it apart if you don't like it. With epoxy, once it set, it will hold. If you do go with epoxy, you also have to use aquarium safe epoxy as well.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Low Tech (1.5wpg PC for 10 hours, no CO2/ferts, gravel substrate), Equipment (72" Coralife PC, Eheim Pro II 2128 w/built in heater, FilStar XP3 w/Hydor ETH201 inline heater), Fish (6*Discus, 2*Angel, 5*Clown loaches, 4*L-018 Gold Nugget pleco, 1*L-260 Queen Arabesque pleco, 7*Cories, Farlowella cat)