can they be tubulars? Mavic reflex's?
Indeed, if you're racing on tubulars and you're putting together wheels specifically for CX training, it makes more sense to train on the same type of tires. A set of Reflex (or Velocity Major Tom, or Kinlin TB-25, just to name a couple) can build up to inexpensive, durable training wheels that aren't even that heavy (depending on spoke/hub choices).
And, while Challenge or Tufo or Vittoria tubulars come in at slightly higher price than clinchers, they will enable you to play with tire pressure in training (which can't be done on clinchers for fear of pinching/burping). That alone is worth a lot of extra $, to be able to really find your limits cornering. If you train on clinchers at 35-40psi and only race on tubulars 1-2 times per week, it's very hard to get used to running realistic tire pressure.
As a final bonus, you'll have a more robust set of pit wheels.