Some varieties of potatoes are more susceptible to rust than others. Can also be caused by alkaline soils. You could try to line the trenches with you first lawn clippings to make the soil more acidic. As far as slugs are concerned, I would dig the planting site over in the early winter to allow the frosts to penetrate the soil to kill the slugs. If you only intend to grow a few earlies, then have another go at the containers. I would say that the secret is to use potato fertiliser as they will be greedy feeders and make sure that they have plenty of water.

Sorry if I'm 'stating the bleeding obvious' but are you earthing up in stages in your containers?

Hya Thanks for all your Answers, and advice much appreciated will try a few of these for one that suits, cheers