Ken,
Migration and solid dialectric insulation, sure, but
it all depends on the diameter of the coil. If you really
wrap the thing tight there's more chance than in a 'looser'
coil. Even in foam dialectric migration isn't a quick thing,
in the solid stuff, it's even slower but it does happen.
Don't count on much performance for your antenna on 160
meters. It may load like crazy, but that doesn't say how it's
efficiency/performance will be. Sort of like a 2" rubber duck
on 2 meters, it works, but not much. But, anything is better
than nothing!
The Century Club is a good place to test how an antenna
works,
lots of stations in all parts of the country. I used to 'live'
on the Century Club when I was working (slow shifts, kept me
from being bored to death).
Good luck with it!
'Doc