If you do go frozen rock hard, add time to the brining. If you can defrost for several hours...soft outside, then it should be fine with normal brine times. Remember to cut back on the salt a bit maybe 25% from a standard brine, as birds are a higher percentage of bone to meat.
When I brine turkeys I brine them in coolers. For warm weather brineing you can add ice as needed.
Also, another thing I do is line the cooler with a garbage bag for brineing and easy clean up. Some may say the garbage bags are not food grade, but I have been doing this for years and I am still kicking !!!
when i do a turkey.........i soak for 24 hours to remove the already added crap, the factory added..........then use my mollases brine, and inject with the brine......but like whats been said, cut back on the salt.......you can get MOST of the added salt out, but not all..........