After basecoating the bases in the mid brown I have been using for this terrain set, I applied the same mix of flock and aquarium sand as for the rest. Still need to better blend in some of the fungi pieces.
I then placed all the parts in their final storage layout on 5mm MDF sheets. For the bases, I marked their position to not play tetris every time I want to store them. The 'trees' are stored randomly, there is enough space, but I covered their MDF sheet in magnetic foil, so the trees, with their metal washer bases, will not fall around in the storage box.
My next job is to paint all the shroom bases and sprinkle sand on them.