A container filled with a gas would be better than a liquid. Something like CO2 or Argon that is heavy will stay in an open topped box even when the gas is warm and it will stay warm easier than a liquid. Using a gas you would only need to heat the bed in order to warm all the gas as convection currents are sufficient, if the bed is not sufficient then a heated container would certainly do. You would have to watch the temperature of the head though if it were completely in the container.

If you wanted to get really enthusiastic you could have very cold air coming out from just below the head like they do in hot volatile liquid wash baths to prevent loss of the volatile liquid through evaporation.

If all else fails just give the whole set up to me, I would dearly love one of those arms. I keep looking for a cheap one on ebay but they are always too much money.