I told the teacher very simply and matter-of-factly what we were doing and why (ie, the fact it was the only week this year that my DH could get a week off), and said I'd send a note as well. The note basically said which week she'd be away, that I'd send a reminder note the week before we left reminding the teacher of the absence so she can prepare the work she wants us to take with us, an assurance that DD will complete all the assigned work and return fully caught up, and an offer to have her do a daily journal with a few sentences and a paragraph about what she did that day.
The journal is something she normally does at the beginning of each class period, but I thought I'd get her a special Disney notebook for it, and after the trip/after her teacher sees it, it can be a special souvenir to remind her about how much fun she had.
I personally wouldn't use the mouseforless excuse letter or compose something similar... it just sounds like you're trying to get away with something that you know isn't allowed, kwim? At least in our district, there are very strict guidelines on what qualifies as an excused absence, and a family trip, no matter how educational, doesn't qualify. DD's teacher, principal, and PTA president all agree that it's just fine to take her out of school for a week for this trip, and that she'll probably learn a lot as well as having a great time, and they know me and know that I'll make sure she comes back fully caught up and ready to do whatever her class is doing -- but it's still an unexcused absence, and they don't have the authority to change that basic fact. (Fortunately, 5 days of unexcused absences means precisely zip at her grade level, so it's no big deal. If she were to get a 6th one, which she won't, we'd get a note from the school board, but that's still all that would happen.)
Anyway, my recommendation is a frank chat with the teacher... no matter what you do for a note, there's no substitute for talking to the teacher one on one.