I need tips for using a castle cake mold?

My son`s birthday is this weekend and I found a really cool nordic ware castle cake mold at goodwill. The only thing is I`ve never used a cake mold. Do I spray it down? Or flour the inside? How much cake mix do I use? If it falls apart a little that`s ok because I`m using white frosting and grahm crackers crumbs to make it look like a sand castle but I don`t want to waste cake mix if it sticks inside. If I spray it is normal pam spray ok? I have that and wegmans butter flavored please help