Installing steam to an sd card?

I've fixed being able to mount my sd card to my laptop (http://ubuntuforums.org/showthread.php?t=2320605 <read this before replying, please. Not to sound rude.), and I currently have 3.2 gigs of storage left on the hardrive. It is a chromebook and I have installed Crouton on it and unity with the ubuntu desktop. Now I caot install steam because I only have 3.2 gigs left on the hardrive, so I've mounted an sd card to it, and I seem to be having trouble installing it to my sd card. (Also, the sd card has 64 gigs)

Any help? That's be great.