[CQ-Contest] antenna advice

[N9GG]

Advice sought for simple wire antenna installation...
We just put up a center fed wire antenna that loaded up OK on 30, 20, 15, 10 for some reason, but poorly on 40 and 80. An external manual tuner helped out on 40 but not 80.
I want to put up a SINGLE WIRE ANTENNA for 80 to 10, or close to it. 20 or 40 is usually where I wind up. Since the ropes are up, center fed is what I want.
This will be for a TS-590SG for a little bit of low power unassisted CW contesting. 
I've had so many antennas and radios in the past, I can barely remember.
Please give me your two cents.
Thanks and GO FRC!!
                                                  Bob N9GG