It should be noted that, in Mars' reduced gravity, it can be presumed the symptoms would be lessened. Still a major concern, however.
Edit: I was wrongly thinking 18mo each way when it's closer to 18mo-ish round trip. Sorry internet armchair soldiers.
You sure it's not 18 months total?
I expect it would be easy to find people willing to make a one-way trip. However, I have two reservations. The first is the acceptance of society of sending someone to their death. The second is whether it is responsible to use essentially suicidal people for such a mission. These missions take a lot of mental resilience, and generally, we consider being suicidal to be a mental illness.