freelance footwear pay rates

I’m currently working as a freelance footwear designer, designing a collection of women’s fashion footwear on a freelance/project basis. A few questions–

  1. what’s the best way to work out payment? In the past, when I have done more casual product, I’m typically paid per construction/per upper on that construction and it’s worked out just fine. However the fashion world seems a bit different with their pay plan.

  2. I’m wondering though, if it’s better to do a day rate? or a project fee? What’s the best way of figuring this out since the projects tend to last over 3 months, on and off, not full time, but I do devote a lot of time to “being available”, never really knowing how many hours it will take in the beginning of the project.

  3. When you travel for development for a project like this, do you charge a day rate while away? in all reality, you could be working at home, if you were home, right?