Dunnage or Cribbing?
In my work, commercial construction sheet metal (high rises and hospitals) we use both terms but they mean different things. "Dunnage" is the term used to describe wood or other non-structural items used to keep materials up off the ground to keep it out of the mud or dirt and to be able to easily get a forklift or hoisting sling under it for the movement of materials around the job site. Usually dunnage is scrap or trash of some sort which has a low cost $$$ or free found on site. Pallets and skids are considered dunnage which are made of low grade materials.
"Cribbing" is the term we use when referring to structural materials used to stack under equipment or other heavy items on the job where there will be crews working under it to protect them from being crushed in case the load shifts or becomes unstable. Working in California we have to always be aware of the possibility of a major earthquake that would cause a load to shift and prepare for it to protect our crews using "cribbing". Cribbing has to be structurally rated materials such as I-beams, tube steel, oak or other hard woods that are rated to support the load. Cribbing is never something just found on site and is purchased or obtained for a specific purpose of protecting our crews. Cribbing is expensive $$$$$$$$ but can usually be saved and reused many times.
As long as you use something as a redundant back up to the jack stands you will be ahead of the game. NEVER use cinder blocks, concrete , or bricks because they may shatter if a sudden concentrated load is placed on them.
Changing the axle on a single axle trailer is probably the most dangerous job to perform on any Airstream but can be done safely if you just plan ahead and take your time. "Don't be in a hurry to get hurt"