I recommend using a variety of veggies for gut loading. I never use spinach, I can't remember why but it's not recommend for gut load. I gut load the feeders with greens such as collard greens, mustard, turnip, dandelion, endive and sometimes kale. I also use bell pepper, carrots, butternut squash apple and orange. You can also buy a premixed dry gut load. Several of the Forums members sale it.
I would also recommend a large variety of feeders and not just locusts. If I have a healthy 11 month old male veiled (not skinny) I feed him 8 or so appropriate size feeders every other day. Please post a photo of him.