Advice needed.

We are trailering two horses out west for a long weekend of trail riding in the badlands of North Dakota. Obviously we would plan a trip with horses durring the hottest week of the century. :-( We plan on riding early in the morning and later at night when hopefully temps aren't 10,000 degrees. And I suppose even if it's super hot, the horses get to stay at a fun guest ranch and get some new scenery.
 So, question is, our trailer has removable upper doors on the rear. Should we take them off to trailer the horses? It looks like this one, but ours has a ramp instead of the lower doors. Would that make them freak out? Last few times Piney's been trailered have been in fully enclosed trailers with the exception of the stock combo, but even that had a full back door.

The trailer also has a vent on the top that can be turned towards the pickup or twards the rear. It looks like this one.

Should we turn it forwards or backwards? If we turn it forward would it create a cyclone like effect in the trailer? There are sliding windows on the sides near the rear of the trailer. I just feel that if we have it forward I don't think it would really do much good...unless we had  a tail wind...

I am an absolute worrier about trailering. I beleive everything that can go wrong...will. I was never like this. I was always so calm and relaxed about trailering, of course it all changed when Piney smashed my head into the trailer. We've been working with the horses but we are also bringing along some tranquilizer that the vet perscribed just in case. I'm not sure if I'm supposed to take an injection or Piney is. Maybe both. I just wish someone would pick up my horse and bring him out there for me. Trailering causes me too much stress...