Got some 1/4 inch HDPE, for the back and to mount controllers. Used 2 pieces. Easy to cut with a hole saw and get screws into. Also quite smooth and was able to use mostly Velcro.
Gotta wait for parts so started to mock up some rock scape. Anyone remember Steve Weast's 450 gallon or so. Loved the canyon he had. http://www.oregonreef.com/sub_gallery.htm
Trying to achieve something similar on a much smaller scale.