Create it horizontally (the type will be rotated). But to view it, choose Rotate Spread View from the Pages panel menu.
I just discovered the 'page tool'. Creating horizontal spines without rotating (rotating doesn't work, that also rotates the baseline grid).
I'm having the same problem, my baseline grid is rotated with the page view.
How did you create a horizontal spine w/o rotating? I'm not seeing any spine options in the page tool menu bar.
Make a spread with two pages.
Don't allow the selected spread to shuffle in the page window.
Now go to the page tool (shift p). Pick up a page with this page tool and give it a new position on your screen, so that the spine will be horizontal.
That's it. Does it work?