[TowerTalk] Dipole fed with balanced line?

[Jim Miller Waco Texas WB5OXQ]

I must move my 40 and 75 dipoles due to rfi in the house that I cannot resolve.  I am thinking about 1 dipole fed with ladder line or window line.  I have 2 possable support points.
1 pair is 126' from end to end and 50' high at one end and 30' at the other.  Second pair 139' apart but 25' at one end and 30' at the other.  The longer but lower is farther from the house by about 10' and runs over level yard with no obstructions.    What is up with the 130' dipole fed with balanced line?   Is this better for a multiband antenna than using 1/2 wave at the lowest desired freq?  I have a MT-3000A Dentron tuner which is supposed to work with ballanced line.  The maximum power I run is 800 watts rms not pep.
Suggestions please.  I have never used a dipole fed with balanced line.  Will the window line take 800 watts or should I get the open wire feeder?  I really only need this antenna to work on 75 and 40.  I use my triband beam for 20+.  How do you bring this line into the shack?  Obviously it cannot touch anything metal along its run.  Is the length of the feeder critical?
Should the wire be long as possable or 1/2 wave at the lowest desired frequency?  (3.9mhz)
wb5oxq