The manner in which the underside of your Gulfstream is constructed would determine to some extent the vulnerability to freezing.
When we were leaving Eastern Canada for the South in March, we would leave empty with all plumbing blown out and P traps containing plumbing antifreeze. This would be the way we stored the coach, in addition to taking precautions to empty the solenoid valve of the ice maker, the 1/4 inch line from the water filter to the ice maker, the valve of the toilet, which is made of plastic and vulnerable and the water pump would have aanti freeze pumped through it.
On our drive South, we usually filled up with water in or around Washington, DC because there would be virtually no chance of sub freezing temps from there on.
I am not sure if your Gulfstream is a fifth wheel, because if it is, I don't have first hand experience with winter travel in a Fifth Wheel. Our travel has been in a motorhome, which we would keep heated at all times while travelling, and the furnaces would heat the underside of the coach where the plumbing and tanks reside.
If your Gulfstream is a fifth wheel, can you keep the heat on while you travel? Is your coach winterized for winter storage?