Did you get and read the rules? Some of the bigger planted tank contests you have to set up the aquarium on site so they know you aren't cheating by having Mr Amano fly in and do your aquascape. I have only been to one aquascaping event that was local, and at that event each person was given the same plants and the same size aquarium to do their scape, but they had over night I believe to get it all worked out and get the water clear. But a friend of mine does these contests pretty often and he says the kind he prefers you bring your own plants and aquarium and set up on site.
If this is not the case then you will want to almost completely drain the aquarium, then cover with some plastic wrap to keep it humid so nothing drys out and dies on route, depending on how far you have to travel, or traffic ( on a business trip in baltimore and traffic is #%^&ing insane ) you may want to take a spray bottle filled with tank water to mist them in route.