[Trapper John]

I am not so sure this is a learned (therefore trainable) skill.

Being able to function at an acceptable level while under stress (hypothermia and/or sleep deprivation) is physiological and highly variable from individual to individual.

I don't know if any studies have been done to evaluate a single individual's variability over time with repeated stress situations, i.e train-ability of the physiological responses. It might be worth searching to see.

My guess is that this testing is primarily to weed out candidates that do not have the physiological make up to function under those conditions.

Your time would probably be better spent in other training where there are documented benefits of the training.