Matt... Drying air might be consuming too much energy, and moisture may still remain.
I have installed low lying loops in 3/4" id, but it must be below frost line, it seems that air makes its way through the water accumulation inside the air line anyway (but it must create friction and some pressure loss, I just cant calculate that precisely..) eventually the low spot will fill with water and the air pressure will push the excess water further down the hill. A drain plug could be a solution (a valve and a tee, open the valve once in a while to flush the pipe... depends on the land shape I guess)
Go for the heavier stuff as it has less chances of being squished under a rock when you bury back the line. I use 100 psi, not the 75 psi.
Also, you could install one of those Koenders freeze kit near the compressor. They are filled with alcohol and when pressure builds up, assuming that ice has formed, a valve opens up and releases some alcohol, minutes later, the ice is gone and pressure resumes. Watch for a good pressure relief valve to protect your pump.
Monitor your pressure gauge to see if pressure is building up� in the end report your findings on this web site
