Caulk is merely the sealant that will keep air and water from slipping between the cracks in the tiny house. If you did not use any caulk, the tiny house would be much draftier and leaky.
This caulk is made to fill voids and seal up the outside of your house. It can be painted easily, allowing it to be covered up and forgotten as the exterior is finished.
Application is very simply using a caulk gun to extrude the contents onto the walls and seal everything up. It is a good idea to apply the caulk right before you apply the trim boards so that the caulk is still wet when the trim is applied. This will further promote a good seal by sealing to the trim board as well as the rest of the house.
On the windward side of the tiny house, it is imperative that you seal up everything very well as this side of the tiny house will be exposed to very strong winds when being towed down a road. Sealing up everything will prevent wind damage from occurring as you tow your tiny home down the road.