On this type of rim, I have had better luck with 4 ply tires. I have a nice 6 ply tire and it's really really stiff, but you just can't practically get it on the rim. It's completely futile. I believe the practical use for that tire is with a split rim such as the glider tail wheel on some models..

What I do know though is just buy the whole tire/hub assembly from monster scooter parts. It's like 10 or 20 bucks,cheap, and works well for a dolly tire.