I'm interested in this myself. I know I would ask for two components: the first is reimbursement for owner's costs that would include movement costs, cleaning of the boat before and after showing, cost for fair wear and tear of people looking at the boat, repair of any damages incurred. This cost is designed to ensure the owner is made whole for any costs they incur in allowing the boat to be shown.
The second would be an owner's gratuity - that's pure profit if you will. This would be designed to "make it worth the owner's time" or to compensate for inconvenience. I'd also base this in part on the duration and whether you moved the boat to the show or if it just stayed in its normal slip.
In a case I'm vaguely familiar with, the owner of a 42' one-off boat moved their boat from a home slip to a boat show in Seattle, left the boat there for around a week and moved it back. I don't know if they stayed on board during the show and answered questions or not. But he did sleep on the boat during the show and had event passes so he could check things out himself. He didn't give me the amounts, but I know he was reimbursed for stationing and de-stationing costs based on hours traveled, the builder had someone clean the boat before and after the show and there was a gentleman's agreement to repair anything damaged during the show. For owner's gratuity he probably got a couple thousand bucks for letting the boat be shown plus free VIP tickets to the event and the builder of course paid the docking fee.
I'd like to hear other's experience. I've told my builder I'd be willing to consider allowing my boat to be shown if we can work out the details.
