On vacation, presumably you would use a water heater that allowed for recirculating in cold water if it got over temp, presumably you could even open a radiator loop for that. The goal is to have something that is thermally stable sitting out in the open air and still can warm water to a usefully warm temperature.

There was a discussion of this sort of thing in the papers on the pebble bed reactor (that reactor uses encased fuel "pebbles" and one question came up with what you do with the "used up" ones.) It has come up off and on both at conferences and in discussion forums.