are you using matte medium, where can you get it other than WS or scenic express?
Yup, I am using matte medium, diluted 40% glue to 60% water.
You can get it at craft stores. The most common is "mog-podge". You could probably get that at walmart.
do you use this for glue for trees?
Yes. I filled up an empty yogurt container with the diluted mixture and dunked the trees in. The sprinkled the foam on top.
Wait so the stuff in the orange bin called mog podge? Is that the matte medium? Could I use this to model water?
Yep, it is matte medium.
I don't suggest using it for water though, as it dries without any shine. For that you should check out "Gloss Medium".