The ethernet cable I used and used to supply with active loop antennas was an outdoor grade unshielded cable. Normal indoor ethernet cable will not last long with UV and rain water.
i often used it laid on the floor or buried just below the grass.
Attaching it to a metal support structure doesn't have any effect as it affects both pairs of the twisted pair equally so if the cable is correctly terminated in a 100 ohm impedance it cancels out any interference or noise coupled from from the metalwork.
Any excess cable can be coiled up. We used to buy the cable in 305m drums. For testing I fixed connectors on each end to measure the cable loss and isolation between the twisted pairs. From memory the loss at 30 MHz over a 305m drum was 10 dB.