I agree with the people suggesting making it into a truss setup. A solid tube 12" is cumbersome, but a truss version is very portable.
Dobstuff for an ultralight kit or a more traditional, beautifully finished SDM are good options here.
Better still, have a go at building your own to suit your specific needs.This is the standard reference:
http://www.willbell.com/tm/dobtel.htm
And this is where you can find the most ATM scopes at the one place:
http://stellafane.org/misc/links.html