That works good. I also make a 'bowl' out of tin foil and cook the fish in that with a little bit of water and lemon juice. Keeps it nicely flavored and moist.
Just buy some aluminum foil and cook your fish like someone smart enough to not cross contaminate your grill.
If you don't, people with fish allergies are gonna have a bad time
If you don't, people with fish allergies are gonna have a bad time