Personally, I use Gorilla Glue and a basting brush. It's pretty thick, so you have to work in into the cracks and crevasses with the brush. The nice thing about GG is that whatever you use to cover it (coco fiber, mulch, etc.), it doesn't have to be dry. In fact, it cures faster in the presence of moisture and the bottle recommends that the surface be damp.

I just recently learned that GG is made of the same material as Great Stuff foam, but not under pressure. It will, however, expand slightly, so after it starts to cure, if you see any of the expanded glue coming through the fiber, you can touch up by pressing more fiber into those areas before it fully cures. You can also touch up after it cures with some fresh glue.

Make sure the foam is fully cured before putting animals in the viv. If you leave the viv sealed for a while and then open it and take a whiff, you should not be able to smell any hint of solvent if it is fully cured. Thicker layers cure more slowly and you can poke holes with a toothpick to accelerate the curing process. Some foam might ooze out of the holes (which is a good thing), and it can be easily trimmed and touched up if necessary.

I actually used the holes as places to anchor bromeliads that had a stem. I just expanded the holes with a pencil and stuck the brom stem into the hole and secured it with a couple of toothpicks until it rooted.

Good luck.