Is this a good idea?

What about using a large livestock-type tub? I know of people that do this for pond fish, and they have wire over it so that nothing can get in and kill the inhabitants. It would be impossible for the turtle to climb out, too. I know that Rubbermaid makes these large troughs; I use one for our horses.
They make very large circular ones. If you did this, it would be cool too because when you move, you could take it with you. You could easily make a land/water area in it, and maybe even drill some holes to prevent flooding when it rains?

I know some people who keep sliders in a kiddie pool (not the blow up ones) or a stock tank. They just add concrete blocks to the middle as a basking platform, some even put a dog kennel with a mesh top over the pool so they are safe from predators.