Growsy,
I live in sandhills, so I understand the sandy soil.
Plant them, put in some manure compost and let them get rain. See how they do in the afternoon sun. They may be alright.
Don't think they don't like water. Especailly in the heat and the sand, if they ASK for water, go ahead and water them. Mulch, mulch, mulch.
Don't water at night, only morning and you will be fine.
Enjoy your dahlias.

The thing about not watering them applies more to those of us with boggy soil. THey do not like to sit in constantly damp soil, but they do survive our rainy climate here just fine, as long as they have good drainiage. I find mine do just fine unless they freeze. NOw that you know they do not want to be constantly wet you will change how you water them and they should thrive. As long as you do not have little slugs or snails eating on them as they sprout, they just reliably sprout and come up and grow. Terribly hot weather may delay their flowers but they usually recover from that. I enjoy mine in mixed flower beds too. After I plant my hundred and 20 or so, I plant left over tubers of my favorites in among my roses and lilies where they put on quite a show of continuous color. Have fun with them!
Which ones are you trying out?

Thank you for the help! I planted them this afternoon. I am very excited, & know I will be hooked if they grow well. It was hard enough making the decision on which 4 to get, then Jan's Country Garden sent an extra.
I picked Carl Chilson, Chilson's Pride, Fuzzy Wuzzy, & Touch of Class, & they sent Sweet Dreams as the bonus. I wanted smaller blooms for bouquets.
Thank you both for the input. I appreciate it!