How do you plan large structures for easy and safe transport to shows?
Compartmentalise

I wouldn't recommend transporting anything larger than a 32x32 stud baseplate. Use Technic pins and 1x2 bricks to connect parts of your model in the same way as the Modular Sets have done. The technique works well for buildings, planes, boats and just about any kind of large model.



Transport

Remove as many small parts likely to fall off in transportation as you possibly can and place them in a sealed plastic bag or other suitable container. Place the rest of the model with the extra parts in a cardboard/plastic box. The box is essential for catching any other fragile pieces that fall off the model. You may also use bubble wrap or tissue paper to pad the box as much as you can. 

Once your Lego model has completed it's journey allow yourself some time to fix inevitable damage. 

Collapsible Structures

This is a fairly novel idea, which I haven't seen done before. Flickr user Legozilla has built a model that is specifically designed with transport in mind. 

This particular design is unlikely to be damaged in transport. The flatpacked version of this model is significanly more space spacing compared to its 'built state' where it's volume is probably 90% air.


  Occasionally, we need to fill in a spot in a display because a member
  needs to be late to a show or some other circumstance. To meet that
  need, I have a couple of buildings that I tote around to fill such a
  gap. This set of buildings is modular, and collapsible so that it's
  easy to transport and flexible enough to fit in most corners of a
  layout. It's also fun to fold and unfold just to watch people's
  reaction.