What's the soil like below your 8" beds? If it's unimproved clay that isn't rock-hard, then you can probably count a few inches of it as part of your depth.
I am growing potatoes and beans in my 3' x 16' bed. In order to hill up the potatoes, I had to steal soil from where I intended to plant the beans. So the beans are basically growing in 6" of good soil instead of the usual 12".
(see the bed on the right; I am growing beans in between the two stands of potatoes)
I hilled ONCE and that's it. Ed Smith in his Vegetable Gardener's Bible does not recommend hilling more than once or twice. The hilling is providing a place along the stem for the potatoes to grow out of, and it is to make sure the growing potatoes are covered so they don't turn green from sun exposure. I don't think you really need more than about 1 - 1 1/2 feet of soil above the seed potato, but I could be wrong.
In other news, I wouldn't quite use the word "devastated", but my potato plants have been hit hard by caterpillars. The same caterpillars that were on my brassicas. I went out this morning and drenched everything in a mixture of neem/pyrethrin* and BT liquid at labeled doses (1 tbsp each to 1 gallon water). That should kill the caterpillars now, plus prevent future ones. I will repeat with BT a week from now.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
By themselves, neem oil (from the neem tree), and pyrethrin (from chrysanthemum flowers) have some anti-fungal and on-contact insect control abilities, but combined, they are some of the best controls organic gardeners have. Unfortunately, I have not been able to find them in a single product and in a high enough concentration to be useful. I kept finding either pyrethrin, or synthesized pyrethroids, and then I'd find neem all by itself.
Green Light is a San Antonio based company that produces many organic controls and solutions to pests and disease both in concentrate and pre-mixed spray bottle form. Recently they came out with the perfect mix of neem (70%) and pyrethrin (.25%) in a product called Neem II, which is labeled for roses, but also lists most vegetable crops on the label. Unfortunately it's $10 a bottle and doesn't last long.
I'd noticed that Green Light had a product with an identical formulation (but as a cost-saving concentrate) called Fruit Tree Spray. It's only labeled for fruit trees, but I called them and they told me off-the-record that it is also usable on vegetables. So instead of $10 a bottle for Neem II, I can mix up probably 200 bottles worth for $15.