Weekly Review
There is no one-size-fits-all formula for developing a new habit. Often I will try one method, abandon it, and then try another.
You might set a goal. For example, perhaps you would be happy on June 30, 2008, knowing that you did 20 weekly reviews. It might help to list operational criteria to help you decide when you've done a weekly review. It might help to state that you are not permitted to count a weekly review as accomplished, if you have done a weekly review 5 or fewer days previously.
You could then create a log with the dates of each completed weekly review.
Some people are helped by announcing to other people their commitment. If you think this might help you, you could start a new thread with your commitment and your operational criteria. You could then create a new post each time you did your weekly review.
From your post, it doesn't sound like you are too busy to do your weekly review. Rather it sounds like (1) it is logistically difficult to do it, because of your extensive travel schedule; and (2) you don't feel like doing it.
Regarding (1), you might alter your tools or buy additional ones that will make it easier to do the review on planes, in airports, etc.
Regarding (2), I often have this problem. I tell myself that it is important for me to feel like doing my review before I do it. The fact is that I can do it even if I do not feel like doing it. Another fact is that once I start doing it, I begin to feel like doing it a little more. So, I try to alter my beliefs. I recognize that it's very good to start things, even if I will only spend 10 minutes on them. I can start things even if I don't feel like starting them, because I will only be doing them for 10 minutes. As others have pointed out, you might do your Weekly Review in smaller bite-sized pieces.
I often find my Review gets spread out over time. Before I can do my review, I have to get my in-box to zero. Sometimes, that takes a very long time.
Then I look at list of higher-altitude goals. That usually doesn't take long.
Then I go through my waiting-for folder. That usually doesn't take too long.
Then I go through my calendar for this week and next. Again, that doesn't take too long.
Lastly, I review my lists of Projects and NAs.
That latter step usually does not take a long time, but it can be emotionally difficult. I usually allow myself to spend a few minutes doing something fun, like visit this forum, after I've completed it.
Maybe you'll get to do something fun, like list another completed Weekly Review in your log.