Looking forwards to seeing finished pieces.
If you haven't already watched the Burma build videos by Mel the Terrain Tutor I'd suggest bingeing them.
Provides a lot of interesting ideas (which you can be translated to a lot of projects let alone jungle ones) and information for using different materials and how to do it reasonably cheaply.
https://www.youtube.com/watch?v=8FTILlx01-Q&t=36s
My personal suggestion is if you want a damp mossy forest, mix water and PVA, paint it on surfaces/vegetation/ground and sprinkle fine turf everywhere.