John wrote:
"---how to keep spacers from migrating..."

My 1970 edition of the ARRL Antenna Book shows how to construct open
wire line. The insulating spacers have holes near their ends and their
ends are also grooved for the line conductors.

A small tiewire is run through the hole and its ends are tightly wrapped
around the transmission line conductors to hold everything in place.

Best regards, Richard Harrison, KB5WZI