Well thanks to the crafty skills of my mate, I finally have one

He has made it big enough so I can fit four 2ltr ice cream tubs in it.
The mixture in which the maggots will be blown in is made of bran, vitamised dry dog food and water.
Although the mixture when wet isn't pleasant to the nose, I know it works very well,
And by the time the maggots are ready to be dished out, the mixture is fairly dry and crumbly - kind of reminds me of the texture of magic sand.
Being the start of breeding season in the next month or so (start of spring) I look forward to giving my breeders the maggots I produce and I'm keen to see how well my breeders do feeding them to their young.
Depending on my success I may not have to use mealworms again.