DaveinPa welcome to the BBQ board!
I've never heard that a gas grill won't yield crispy skin on chicken. I don't have a gas grill but I would suggest cooking chicken on a medium heat until it is done then turning the heat up near the end to crisp and brown the skin.
For coke can chickens, I've never had crispy skin. It's due to the low temperatures at which it's cooked along with the moisture from the water pan and cola. We rarely eat chicken skin anyway and the dog loves it. So I've never tried for crispness.
Here is a previous discussion that mentioned crispy skin: Chicken and the indirect method
For additional information do a search with the following parameters: “crispy AND chicken” (include the word “AND” in upper case)