Hypothermia is a downward spiral. Even mildly hypothermic victims are not capable of keeping themselves warm with just a insulated blanket. An additional heat input is required to reheat the hypothermia victim. This is going to probably be one of your main challanges in terms of survival equipment aboard a liferaft. A warm sugary drink (hot chocolate is best) and a set of dry clothes is required together with an insulated blanket or bivi bag which is large enough to accommadate 2 people - the hypothermia victim and the fit crew member who is helping to provide some additional warming.

Perhaps you could include in your survival package a specific hypothermia kit consisting of the following.

Blizzard Survival Tube.

Vaude Stormy Compact Hanging Stove with a Primus Aluminium Gas Cartridge.

Sigg Oval Bottle with neoprene bottle cover which allows the bottle to be used as a hot water bottle.

Smartube with Sigg Bottle adapter allows the hyperthermia victim to sip hot liquids whilst the sigg bottle warms the victim.

A pair of Neoprene Gloves.

Hot chocolate or hot soup sachets.

Dry clothes set. Vacuum packed Snugpak Softie top and bottoms.

All in a Ortlieb type Dry bag with grab handle (heavy duty).