Bob, K5QWG wrote:
"Or should I go buy some bare solid copper wire?"

Depends on frequency. As a path for electricity, the earth is like a
leaky capacitor or a good capacitor in parallel with a resistance.

Terman says on page 807 of his 1955 edition:
"At broadcast (550-1600 KHz) and lower frequencies the ratio of
capacitive reactance of the earth to the earth resitivity (sigma
reciprocal=1/conductivity) is considerably greater than unity, so to a
first approximation the earth can be considered as purely
resistive.----Conversely at frequencies of the order of 10 MHz and
greater, the impedance represented by ground (not sea water) is
primarily capacitive, and ground-wave attenuation at a given physical
distance is determined by the factor of frequency divided by the
dielectric constant plus 1."

So for low frequencies use bare wire. For high frequencies, you won`t
notice insulation on your radials, electrically.

Best regards, Richard Harrison, KB5WZI