Cant help you with the mount other than to say you might be better off going to ArchosFans.com - News, Rumors and Reviews
and looking at the a70 case thread.
I have the 8gb a70 with a 2gb sd card. I have loaded 12 movies, tons of songs, and 40+ apps. No issue yet but I'm sure it's coming. I'm getting a 32gb card shortly. The unit was dropped 1 time from kitchen counter height. Would a spinning hard drive have survived? Not sure.
Must have app: Handcent, Currents, Google Listen, Tapatalk, Sipdroid, Dropbox, Newsrob, Google Voice, Evernote, Astro, App Organizer,iHeartradio, Picsay, Shopsavy, Skype, Wave Secure, Timeriffic, iGolf, Egnyte, Google+.