Len,
Glad to hear you're looking after your physical fitness as well as everything else (too many pilots obsess over checkrides, training, company policies, etc... and forget that you can be God's gift to aviation and it won't matter at all if they lose their medical).
I run marathons. Not as much as I'd like anymore due to marriage and a kid on the way, but as far as the running goes, it fits in well with the NJA lifestyle. Almost every hotel we stay at has at least a decent treadmill. Yeah, a couple have crappy treadmills, but they're few and far between. And of course, many places you can just run outside. If you're serious about your fitness, I imagine you have no problem running outside in the cold as well as the heat. Personally, I enjoy a nice quiet run on the backroads while a pleasant snow is falling.
I will repeat what others have said, if you're serious about your training, you'll find the time to train. I'm currently training for the Pittsburgh marathon. I've put together a training program I think will get me to the starting line and be able to finish in under 3 hours. On my last day of my last tour, the only time I had to run was at 0345 in the morning (needed to get an hour of running in). So guess where I was at 0345? Down in the workout room on the treadmill.
There is a caveat though. Always remember that while on the road, the job comes first. If you have a schedule where you'll need to be rested (maybe scheduled for a 14-hour day after you just flew a 14-hour day) you may have to forego the workout in order to be properly rested for your trips. This has happened to me on more than one occasion. But it doesn't happen every day, and doesn't seem to have much of an impact on my training because the rest of my training is pretty regular.
Good luck with the racing!! Oh, if you're looking for a great marathon to run sometime, try Chicago. I may be back there myself in '09. But I've already run it 6 times.