Peace on earth.
There is no hard and fast rules one must follow. There is nothing wrong with your approach. You are the owner/captain , you control the deal. I am just a by-stander happened to pass by.
Let's set your case aside. Crews pay for fuel and boat expenses often if the trip is for pleasure. For example: The owner offers a RT voyage from SD to Hawaii. He may or should charge the crew for paying his share expense including fuel and marina charges that incurred during such pleasure voyage.
OTOH, If he is a delivery captain or he must move his boat to Hawaii from SD regardless if he has crews or not, he should not expect the crew to subsidize his move even the crew may get some pleasure or experience out of this deal.
Likewise, the captain should NOT expect his crews come in a few days early to slave them to do repair work and clean his boat before the trip. However, the crews are expected to maintain the proper order of the boat to its original condition before they leave the boat.
It is all about fairness and reciprocity. Having said that, there are many exceptions.
Fuel cost is often insignificant with good weather and wind. This will change quickly with head wind and urgency.
I read, think, and act independently; I don't come here to win a popular contest, nor I am here for free sex. I come here to learn, be challenged and be inspired in the art of safe off-shore passage. I am NOT afraid of dying in the sea, but I am afraid of dying in a nursing home and burdening those who I love.
I am old school; doing the right even when no one is watching is important to me.