Hey Glen (or anyone else):
There is no way in hell I will trust cast rims to suffer the punishment of my fat ass continually crushing them into the ground! Is there a reason that escapes me why I couldn't successfully seal the spoke nipples with a good quality vinyl duct tape? I can't believe it wouldn't hold pressure for the day if applied with a little care! A hell of a lot cheaper than off-the-shelf tubeless rims too!
Yes, I'm aware I would find much greater weight saving if I focused on eliminating the large tire around my middle rather than worry about the teensie, weensie weight difference of a couple of wheel tubes! But wheel tubes are unsprung weight!