Domain or Workgroup

I have the task of implementing a number of new laptops and tablet PC’s. All of these PC’s will be geographically spread out and none of them connected to a physical network. Very rarily will they actually connect physically to our main network. Security is of a concern to us.

Should these PC’s be added to our domain or should these just be on a workgroup. My reasoning for the domain would be for security purposes. We are running Windows XP on all of these PC’s.

Cheers