Used my 400h from UK to French Alps in the winter. Glasgow to Courchevel via Hull / Zeebrugge and back with roof bars and a ski rack, at French M/Way speeds, gave an average of just over 25mpg (UK), which I felt was pretty good. Comedians - check your tyre pressures - the RX fuel consumption is very sensitive to low tyre pressures.
The consumption does drop in the winter, as the motor has to run more frequently, to keep, principally, the cat convertor warm, but also other engine parts - so I was reliably informed by the dealer.