How are they with travelling normally?
If they've got beds/blankets/cushions/things they already sleep on, put that in the box with them. It's something familiar and safe. Leave the cat boxes out and open for a while before the move so they get used to them. Maybe do a couple of short trips beforehand if they don't travel much.
We did a 2.5ish hour move, the cats spent a couple of days in a cattery while the packing and stuff went on. Decided that the cattery (which they'd been to several times before) was likely to freak them out less than all the stuff in the house disappearing into boxes. Actually they stayed there until we'd moved and unpacked, we went back for them the following day.