Either would work. The last I did I rubbed the turkey while dry. Later I have read about coating it with mayonnaise. Sounds good as well.
Your tastes are your guide. Both the butter or oil would be good though.
When I get home I will look for a good rub I have used in the past. The one I currently use is Jeff's rub which is not mine to give out. You can buy it from this site though. It does have some spice to it but that can easily be changed with you modifying it to your tastes. Buying the recipes also supports this site which make them worth it alone, add on the fact that they are VERY good and you have made a very worth while purchase.