Not too complicated at all! They are giant "EarthBoxes", and I made half a dozen "EarthBox" clones at least 10 years ago, much smaller, out of 18 gallon Rubbermaid totes... they work great! You're going to love them!
Just make sure you drill a drainhole in the outside tub, just below the lower level of the soil, so the roots don't drown if you get heavy rain.
And if it gets very hot where you are, you might want to spray the outside a lighter color, so you don't cook the roots. They have spray paint for plastics now... I've painted several harshly colored large plant pots so they blend in better.
Summerthyme