Marketability of RNs in clinical research positions.

Pure nursing research is very difficult to find. In my experience, nursing research - i.e: intervention testing/evaluation, efficacy measurement, outcomes, theory...etc. is conducted by academic nurses - professors etc. in addition to their teaching duties, or by grad/PhD students, in addition to their studies; or by nurse executives, in addition to their other duties. Many academic researchers receive grant support through professional organizations (AACN, WIN, ANA, etc) and the NIH; and use the funds for tools, assistants, statiticians, document/poster preparation. I have never really found a position as a pure nurse researcher, as an a assistant - yes (many of my mentors came from this role). I now struggle to try to conduct independent research, and write, but find myself time strapped - full time nursing research in a paid position would be nirvana.

How difficult is it to get hired into a CRA or clinical research nurse position with an RN, BSN, no experience working as a CRA, but with training as a CRA or CRC? What's the differences in CRA, CRC and clinical nurse researchers?

Don't jugde research jobs by their titles. A CRA position might be a data manager at one facility and a regional monitor at another. You really just have to look at job descriptions. I hold the position of RN Specialist and my data manager is a program assistant. You would never know we held resarch jobs.

How difficult is it to get hired? Depends on the market in your area. Most people get hired based on their clinical background. Getting certified in your area will probably do more for your marketibility than taking a course IMO.