I think you need to make a contract to avoid problems. Sometimes, there is an accident and the question remains outstanding : "Who is responsible in case of accident?" the contract is here to avoid this kind of question. In which you define clearly all the aspects to your half-board. Who pay what (for example dentist or veterinary,...), the distribution of days, how use the material placed at its disposal. And what the half board can do !
You can find half-board in your club or in different websites such as federation, association, breeding farm, ...
I hope I helped you, Bye.