I often travel with the Alde boiler filled with water; it depends if I need hot water in the next few days or if I am intending to lay the van up.
The Alde's inhibited water circuit remains filled throughout the life of the particular antifreeze/ inhibitor it is charged with. [2 or 5 year life fluids being the more common].
Recharging this can be challenging, it is definitely something that would not be drained until it is time for it to be changed.