Pat, the correct length for a feedline is that which reaches from the feed point
of the antenna to the terminals of the tuner.

Having used the Dentron Supertuner I doubt if you'll have any trouble matching
any impedance you'll find at the input of the feed line.

If it doesn't match on any particular band there are four ways to achieve the
match, depending on the specific impedance at the input of the line. Try a
series cap in the line, or try a parallel cap across the line, or do the same
thing with an inductor to see which works. It's cut and try, but it's better
than having the line coiled up in the bathtub.

Walt, W2DU