Friend has done it north of Seattle for years. Last time I visited was including a circulating ventilation system that used the hot air between the outer covering and the soil to heat the soil.

Thanks for response bboy, but I really have no idea what you're tryin to say ?! Your friend heated the soil with some sort of system ?

In our 4-H garden, we had Yellow Doll ripen without any protection. Accidently piled some darkish wood on the north side of the watermelons and they really warmed up.
This year we will use a small hoophouse, black plastic to warm the soil before putting in seedlings and use the dark wood once it gets warmer outdoors. The kids will start the seeds next week in a greenhouse.

Great to here cedar wa ! I think I am going to try to grow them this year

Yellow Doll and another orange-fleshed small melon did well here several years ago with no coverings. Started indoors with heat. Planted out early June, ripened in late September.

These are the small "icebox"-type melons, the bigger stuff will likely need all kinds of coverings.

Cottontail melon did well.

I planted the heirloom variety in 2012 (doing again this year-13) right on the ground, uncovered and it gave 3 watermelons! I was told to get the variety called "Sugar Baby". Although it didn't ripe on the vine, I picked and left in the counter in my kitchen and in the end of Nov. beginning of December I cut it open and it was red, flavorful and filled with seeds :)