I’m a little late eh. Lol. ok, i use a low poly tunnel made with pvc hoops and a beam. About 16’ wide 20’ long is enough. Soil same as pumpkins with more perlite. The secret is warm soil. Soil heat cables and plastic mulch. Drip lines underneath. Watermelons survive hot temperatures but like it about 28 c. Nights are tough for me but 16c did it. Heaters at night for me, cooling vent fans during the day. need a nice size plant before transplanting, should have a vine starting. Get it out in early April pollinate in mid June on one of the large vines. Keep the plant dry. Those vines rot easily. Most of the time temps too hot end my season. The rest of the bad endings are caused by too cold of temps. Thats the problem growing in a climate that has a short intense summer. Cool summer's are better because I can heat air easier than cool it. At the beginning of every season I feel like an expert and by the end I feel like a green rookie lol. Think about that before taking my advice.😜