Um, yes and no on the trailer. Depends, parking and RV camping around there can be pricey, but so is a hotel. And permits for camping down IN the canyon are often a wait list, a very long one. But it's lovely there! And if you decide to stay.... stay or RV in Page. That would be my advice. It's right on the Utah border, just north of the Canyon. And it's also right there at Lake Powell. March will be too cold for swimming, but the fishing is always good!
And since you are reqally likely to catch some catfish, or even trout, the kids will have fun with it.
In the canyon, there are mule trail rides, lots of view points, helicopter and small plane tours that fly over the canyon(AWESOME).
And in addition, you can ride the renovated train from the Canyon to Williams and back. It's very cool, the train gets "robbed" and all sorts of things. It's excellent fun! There's food served too.
Hmm, let me see if I can think of anything else.
I'm right here in Flagstaff, so there's lots in Northern AZ I can let you know about mama!