Most of this is handled (Though admittedly not in detail) in the environmental rules for cold:
Cold and exposure deal nonlethal damage to the victim. A character cannot recover from the damage dealt by a cold environment until she gets out of the cold and warms up again. Once a character has taken an amount of nonlethal damage equal to her total hit points, any further damage from a cold environment is lethal damage.
An unprotected character in cold weather (below 40° F) must make a Fortitude save each hour (DC 15, +1 per previous check) or take 1d6 points of nonlethal damage. A character who has the Survival skill may receive a bonus on this saving throw and might be able to apply this bonus to other characters as well (see the skill description).
In conditions of severe cold or exposure (below 0° F), an unprotected character must make a Fortitude save once every 10 minutes (DC 15, +1 per previous check), taking 1d6 points of nonlethal damage on each failed save. A character who has the Survival skill may receive a bonus on this saving throw and might be able to apply this bonus to other characters as well. Characters wearing a cold weather outfit only need check once per hour for cold and exposure damage.
A character who takes any nonlethal damage from cold or exposure is beset by frostbite or hypothermia (treat her as fatigued). These penalties end when the character recovers the nonlethal damage she took from the cold and exposure.
Extreme cold (below –20° F) deals 1d6 points of lethal damage per minute (no save). In addition, a character must make a Fortitude save (DC 15, +1 per previous check) or take 1d4 points of nonlethal damage.
A lot of this is vague and open to interpretation. Partly, that's because it's not a focus for most campaigns. There's a lot of GM's who'll just let you travel through cold areas with either Endure Elements or a Cold Weather Outfit.
Note that all saves happen because of a lack of protection. If the party uses Endure Elements, that stops them from having to make Fortitude checks unless circumstances go really extreme. But if they don't, then the GM will have to make a ruling on how much blankets and such help against exposure. For example, you could make a save every two hours instead of one, or give a minor bonus on those saves. Or when using sufficient blankets and sharing body heat, saves might not be required at all.
Somewhat less objective, I'd personally rule that having two out of three (tent, blanket, campfire) would stop you from having to make saves during the night. Campfire can help you warm up, and therefore heal from the exposure non-lethal damage while traveling.
It's important to keep in mind what is fun for your gaming table. Does your party like having to micromanage a lot? Then make a detailed ruling so they know how to prepare, and how to act it all out.
Are they just there to slay dragons and get loot? You might want to just handwave it away.