Although the Dually rim is touted as tubeless ready, it does need a bit of sweet tape lovin' to get it nice and tight. Especially if you choose to run the Knard in the lower tpi count, which is NOT considered tubeless ready.
The biggest issue I've found with this rim is that it uses a bead "shelf" rather than a bead seat. The shelf does not grip and hold the bead of the tire, encouraging it to seat into the sidewall and protecting it from lateral loads during riding.
To deal with these issues, here is a strategy that seems to work very efficiently.
First, apply some Stan's yellow tape to the center of the rim, effectively sealing off the spoke holes per standard protocol.
Next up, we are going to create a slight raised section on both sides of the rim to encourage the tire bead to stay in place. I grabbed some Gorilla Duct Tape, a nice heavy and easily applied product, and cut two strips about 4mm wide, placing them around the rim about 4mm from the sidewall. Just enough room for the bead to have a little wiggle room while seating the tire but not so much that a strong lateral force will force the tire off of the bead shelf.
Then cut some tape to the width of the rim, running from sidewall to sidewall with no material moving up the vertical surface. Two strong wraps around is all you need.
Use an Exacto knife to clean out the valve stem hole and insert your tubeless valve stem and tighten down. I was able to easily air these up with a compressor, had to work just a little bit more with a floor pump. I seated them with air only, then added fluid through the valve stem.
Super easy and ready for nasty trail.