Well, first of all the only why to securely anchor the bags to the back of the saddle, will be to take the screw conchos off the back, and put the bags in between the conchos and the saddle skirt... its not the best way, but I've done it for customers before. If anyone else has any better suggestions, I'd LOVE to hear them!
The other option is to replace the back conchos with slotted ones, and instal strings - but to do that properly would involve drilling through the tree.
Also, its a good idea to anchor the bags down to the back cinch, so they don't flap around.
As for treatment, I'd dye them as close as possible, then oil then lightly (they will darken...) then i usually use atoms wax...
You need to consider:
- What will they be using the bags for? Long weekend rides, or a few hours out? Long weekend rides need strong and durable bags, with better treatments. Weekend "ditch rides" can get away with a tad less quality and more money into it looking pretty... but I all comes down to a compromise between what you're willing to put out there, with your name on it, and what the customer is willing to pay for, and wants.
- What will they be keeping in the bags - so you know what sizes
- What type of closure do they want? Buckles? Snaps? Ties?
- How do they value aesthetics vs function?
- HOW MUCH ARE THEY WILLING TO SPEND