As long as you have no knowledge that the person you sell the gun to is legally prohibited from owning firearms you can sell it anywhere you want in your home state of Iowa.  Sell it at a garage sale if you want.  Selling to a person who can show an Iowa purchase permit, or carry permit would help your confidence level if you are afreaid of who may be buying.  You won't get top dollar from a dealer at a show, because he will want to pay less than dealer cost of course, then you used the rifle, so he will want to pay less than that even.

Nothing you are legally required to do, how ever much documentation you decide to do is up to you, you are the seller you get to set the rules of the sale.