I used the method above with Schwalbe BMX tubes.
A doddle to do & have lost no air at all since I did the conversion back in January. Rims are X719’s with Michellin All-Mountain 2.2’s.
Have been playing with lower pressures. Had them at 25psi but there was too much drag on climbs so have settled on 28psi. At that pressure there’s loads of grip. I’m 16st so pinch flats at that pressure would normally be inevitable.
Best tip…press the tyre against the rim around the valve as your pumping.
Plenty of people on here will tell you it cant be done unless you throw £100’s at new wheels & £50 tyres.