MonsterZero,
I can't describe the weathering process 'cause I didn't do it myself. But my modeler
who did that JS-3M once wrote an article on "Making of the Famo" which I translated
into English and made available at :
http://www.falconbbs.com/famo-eng.htm
and since the Famo was painted in one color (grey), the process was probably the
same with the JS-3M which was also painted in one color (green).
As for the background, I used a 60x120 cm artificial grass sheet (Made in Germany)
and a 40x60 cm artificial pebble sheet (made in Thailand). I once wrote an article
"Behind the Scenes" about the equipment and process in photography, available at :
http://www.falconbbs.com/behind.htm.
Happy modeling and photography!