Nope, NO dry spots. If you're getting dry spots at all, then the saddle doesn't fit. If it slides back, then you're putting it too far forward, or your horse has a serious lack of muscle behind the withers.
A great solution for wither hollows is a Skito Correction saddle pad
. They have a shim made just for that issue and it works really well. My DH's gelding has the same problem and with the right shims, his saddle fits a LOT better. You use the Skito pad over a saddle blanket or thin felt liner pad (1/2" or thinner).
I would recommend against Royal King saddles. They are imports and not good quality. The auto-adjust tree can "stick" and break pretty easily. I would look at quality older used saddles. You can get a good older Circle Y or Textan for around $300-600. My Full QH Bar Circle Y fit my wide mare well. My DH's gelding goes better in older Semi-QH bars.