What variety did you grow?

I get huge potatoes here. The problems here are voles and scurf.

They were Beauregard, Centennial & Vardaman. The few we did get rotted quickly.

I just planted slips that grew from a store bought sweet potato. I rooted them in water in a north window first. I planted several different times. We have slightly amended sandy soil. I fertilized once with 10-10-10 and watered when it hadn't rained for a few days. I had huge taters. I got about 35-50lbs. I even got tubers where the vines had rooted. They weren't very big, but I saved them to plant in the spring. I only had about 7 plants. Of course each hole had about 12 slips planted in it. Not conventional, but it worked great for me.

Has to be the way you had them positioned - may have been just way too droughty. Try ridges next year, the standard technique you can read about on any land-grant U home-garden webpage.

When and how did you plant them?

I think the enclosures got too hot, so the plants didn't initiate tubers. I'm in a cooler climate, and sweet potatoes size up nicely in soil 15 degrees cooler than what you had in your tires.

I use chicken wire fencing with skinny stakes (some folks use driveway reflectors) to keep chickens and dogs from going where they should not. I let pumpkins or winter squash run into the sweet potato vines, which helps hide them from deer.

We didn't have drought as I watered when it didn't rain. I thought they loved hotness but you may be right about the heat causing the tubers to fail. Also, read about them failing because of a lack of phosphorus and I know we were on the low side.
I think I will try hills this year and just use some from the grocer which buys locally and ammend beforehand to make sure the soil is just as they would like! Oh, and they also said too much loam could cause them to fail.
I also had them planted in with pepper plants. Maybe they don't like peppers...hhmmmm?

Doodlebug
This was my first attempt at sweet potatoes also, and a bust. I grew slips from organic store bought sweet potatoes. I harvested a bunch of them about the size of the petite gourmet potatoes at the grocer. I planted some the raised beds now so we'll see if they fair better. Check out Debra Graf's website, she can grow some nice sweet potatoes.
Craig

Here is a link that might be useful: Mini Garden Abundence sweet potatoes

Did you wait until frost to dig them? That could be why the ones you did get rotted. Were there a lot of weeds? I grow mine in black plastic. Did they get enough water? Root veggies need the most. Did you do a soil test? Your ph may be off; they don't require fertile soil.