Meltric has a scheme dialed in for industrial motors.
Though not well shown in Meltric's photos, their device is obviously suitable for strain relief modification/ enhancement.
Other NEMA players have directly competing products -- and all should be examined.
Hubbell makes a slew of Kellums style strain reliefs -- suitable for SO cord -- and much more.
Strain relief can be added on to Sealtite whips, too.
Use Sealtite angled fittings -- angled at 45 degrees, that is.
These can kick the passage of a whip clear of trouble -- where a straight or 90 did not.