After Historicon, I'll need to build some panel storage racks but thats a project for another day.
Woodland Scenics Static Grass - 2 parts Light Green (FL364) and 1 part Dark Green (FL636). The affix the static grass to the board I put down a think layer of undiluted matt medium. Work in relatively small areas (18 x 18 inches). The static grass is applied by placing it in an old wire mesh strainer which I tap against my hand (like a terrain making tambourine). The strainer is held about 3-4 inches above the panel. Once one section is done move onto the the next.
When brushing the matt medium along the edge of an existing section it's best to only brush away from the sceniced portion (in the second photo it would be to the right or top of the picture frame). You'll pull some fibers into the new area but those will get covered up by the new layer when it's applied.
You can also use standard white glue as an adhesive. Ive found matt medium to be a bit better as it never yellows - sometimes white glue will yellow over the passage of a few years.
You want to wet the top but not soak it - if you've got water dribbling off the edges of the panel then you've put on too much. It's not really a problem but greatly extends drying time.
I use spray bottles from old household cleaners to apply both the water and the diluted matt medium.
Please notice how I've pulled the panel apart - thats so they don't get "glued together" while the matt medium dries. As with most useful terrain making hints, I've learned this one the hard way.
Bragdon Enterprises for my model railroad. It's easy to apply - just put a little in the center of the crater and rub it in - the friction from the rubbing causes the material to adhere to the surface.
Let me know how you think the craters came out. In the fall, I'm planning to do a "WW I themed panel" with trenches and craters do this was a little bit of a test.