My apologies for my tardiness in updating the bulldogtrust site.
I am too skeptical to try coax inside one side of the loop tubing, due to high voltage and asymmetrical capacitance it would introduce at the exit point.
My simple minded solution, discovered first on a Russian website, uses capacitive feed at the loop's tuning capacitor. Each side of the tuning capacitor is coupled to each side of the coax through 10-50 pF of capacitance (depending on band and loop size) per side to match 50 ohm coax. With a kilowatt there is 6 or 8 kV difference between loop and coax there, so high voltage high Q capacitors are necessary. A practical solution is a series string of 3 or 4 small inexpensive USSR surplus doorknobs on each side of the tuning capacitor. A a series string of 3-5 39, 47 or 100pF at 3 kV from Ebay will provide trial and error tapping choices for getting a match. (I use a 15 kV vacuum tuning capacitor to handle my kW amp)
Hung from a tree branch, the capacitor at the bottom of the loop should have sufficient distance to ground to be both safe and efficient. (1 diameter is usually sufficient)
Incidentally, a reasonably efficient loop will be too sharp in tuning to use a DC motor. Stepper motors (NEMA 17 is sufficient) and controllers (T-500) from pololu.com with a generic quadrature rotary encoder is one way to go.