I'm gonna go with a marrow sun kit now that I have a fiberglass helmet with aluminum stalk and improved visor. It will make the inside a work of art as well. but if it doesn't take up enough room I am gonna use well cut and placed weather stripping to augment it to fit my small head.
I just got done doing mine , I used foam stripping I molded a down ward path for airflow around the the sides of the visor. It allowed me to tailor fit the helmet to my own head. my fan points at my brow in down ward anyway so that helps vent air out.
I hate the hard had method because i always seem to lose hair every time I pull off the helmet. I wore one of these for a couple of years just out of high school.I have never tried the lining/ padding of other helmets but I would bet any of the three would be a good way to go.
I have two hard hat liners and plenty of foam, a Mystery buy'ce, and a fairly large head. Also I plan on running at least some rudimentary electronics inside too. I think I'm going to have to probably work with the foam as the hard hat liners would take up too much room, no?