well, Dill, I am tempted. I do have a new garden that is beach sand (I
dumped several tons of compost on it), and next year I do want to grow
either melons or watermelons. But will melons grow in sand (heavily
mulched/composted)? What about vine borers (plentiful here)? And twice
a week watering too much? Sand in midsummer around here dries in two
days.. (this is Michigan, Zone 5.5). Oh, and finally: what about cover
(hoophouse) for early starts? Does it help? I do have that.

1.Watermelons will grow on a sandy soil so poor that it won't sprout Blackeyed
peas. They have lots of feeder roots that extend laterally the lenght of the
vines and if conditions are suitable down to six feet. They need aeration and
cannot go deep into a heavy soil. An old sandy field that won't grow hay, with
the addition of 300lbs /acre of 10- 10 -10 grows beautiful watermelons here in
GA,
2. Squash vine borers don't bother watermelons. The only insect problem that
has been serious in over 60 years is the striped cucumber beetle. They do most
of their damage to emerging seedlings.
3. Watermelon is a heat loving plant. When I lived in Virginia, I did
experiment with hot caps to get a faster start. On average I could gain about
10 days. Never tried hoophouse or polytunnel culture. Should buy you some time,
but only you could decide if it is worth it.
4. SInce you are in Michigan, I would suggest you start with a small short
season cultivar. Yellow Doll (yellow flesh) and Tiger Baby(red flesh) come to
mind.