Hello Owen,

You are right, feeding in the middle is good, your feed line is in the
symmetry plane, where you have no E-field component parallel to your
feed line. The line itself will not distort the radiation pattern.

When it is a halve wave mono band antenna I would use a coaxial feeder
with balun (current mode balun with ferrite cores for example).

When the antenna has to work over multiple bands, you get problems with
the impedance when your dipole is a full wave. Matching the coaxial
feeder/balun combination will make almost sure all your power will be
wasted in the form of heat in the balun and or the coaxial feeder. In
that case I would prefer a symmetrical line (can have extremely low
loss) and a symmetrical tuner.

When one end of the dipole is close to ground or a large metal
structure, you may feed the dipole at that end as an alternative. When
your dipole is a multiple of halve a wavelength, the input impedance at
the ends is in the high kOhm range. So you will have a relative low
feed current and therefore also low ground current (so the ground can
be relatively bad).

I hope this and the other replies will help you to make good decision
on what to do.

Wim
PA3DJS.