Coiling generally negatively affects high frequencies, but this should not be an issue for a subwoofer feed.
Very true. Coiling increases inductance. The series impedance (something like resistance, putting it a little simplistically) which would result from that inductance is directly proportional to frequency, so it should be insignificant at deep bass frequencies.
Apart from the coiling question, though, I would suggest that you try to determine the d.c. resistance, in ohms, of the 25 foot cable length (actually, 50 feet for the round-trip). That would be dependent on the gauge of the cable; if you know the gauge you can look up the ohms per foot in standard wire gauge tables on the web. If that resistance is more than a small fraction of an ohm, it could affect bass damping. If it is in the range of, say, 0.1 to 0.5 ohms or less, then it should be no problem since that would be a very small fraction of the subwoofer impedance.
Regards,
-- Al