I don't have experience with a port catheter for IVIG and I am not a medical doctor. However, if I were you, I would NOT consent to a port catheter unless it was proven to me that it was absolutely medically necessary.
There is a lot of information on the risks and benefits of ports on the Internet, so start your research there.
Then, I suggest that you ask your nurses rather than your doctors about the pros and cons, because they really know, and are more willing to talk, about what happens to patients when they get a port catheter.
I have asked my nurses about ports from time to time during the past nearly 10 years that I have been receiving IVIG, because at first thought it seems to be such a simple and convenient solution, but they have all told me the same: Do NOT get a port catheter unless all other options have been exhausted.
Why are they more willing to spend time and effort looking for my veins every month rather than connecting easily to me via a port? Because (a) they know and are more willing to talk about what can go wrong with a port, and (b) they really care about their long-time patients -- more than doctors do.
Anyway, think about it: If you don't absolutely have to do it, do you really want to have an extra opening into your body that can become an autobahn for an infection straight into your vital organs?