craftgrrl | Your Tote Expertise, Please!

This is my second tote made with SuperEggplant's incredible tutorial. http://www.supereggplant.com/archives/000216.html

I have seen the light and begun to use interfacing..the first tote doesn't have any and is quite floppy.

My urgent, burning question is thus: if I am making a reversible tote, do I need to put interfacing on both the "lining" and the "exterior" since they could be reversed? Or is one interfaced side enough? Or do I just need to calm down...hmmmm

Thank you all, and I aspire to be as crafty and talented as you are...someday ;)