Matt,
I just had one a week ago. I did not have an erection problem and my guess is that you won't either. It is a very simple procedure. Yes, you have to undress and wear a gown. (It is the similar as what they do to check on pregnant women for their babies in utero.) They slather your scrotum with a gel-it's cold. I had mine done at a clinic by a woman technician. It takes abut 10 minutes or less. Mine was done because I have an enlarged left testicle. This is the second time for the procedure for me. It turned out to be a hydrocele (a fluid sac around the testicle.) Mine was more solid this time. Before, when I first noticed it a couple of years ago I noticed that it was larger and squishy. Mine is not a serious problem, but my Dr. has referred me to a Urologist for a consult. I don't know what that will be about yet-maybe using a syringe to draw the fluid out?? It does not affect me as is-but probably a good idea to follow through on.
I hope your is as easy as both of mine and I wish you good luck!
Jim