I also wanted to do the DIY mugs, but it was just a nightmare! The paints kept rubbing off my sample mug and washed off in the water. I even used an etching product for stainless steel, but it was so messy.
I ended up ordering my stainless steel travel mugs from discountmugs.com If you join their mailing list they'll send you coupons for 10-25% off the regular price of the mugs. If you live in the US, you can often get free shipping too.
I should get mine next week in the mail, I can hardly wait! When I get them in, I'll post pics for you to see.