Roasted chicken ends up only salty outside
Not trussing is not your problem. I don't always truss a bird and often spatchcock (butterfly) them. I don't find that it makes a difference in the seasoning either way.

What I suggest is to season inside and out, but with about twice as much seasoning on the inside. Then season under the skin. Let the chicken set for about 30 to 40 minutes before cooking.

You may consider adding a small amount of stock to your pan. (I usually put about 1/4 inch.) 

I usually start any whole bird breast side down, flipping half way through cooking.

Lastly, you may want to consider lowering the temperature and cooking it a little longer.