So I've finally completed this, after no end of trouble getting a PC with 8Gb of RAM to let me Photoshop the 188Mb stacked CR2!
Ended up buying portable camera tripod for circa $100 works great for such short exposures and far simpler to transport! This was 4 x 10s F3.2 in my suburban backyard, but plan to travel around a bit now and find more interesting terrestrial landmarks
http://tinypic.com/r/24qskcg/5