Hello,
I'd like to give you a hand. Could you tell me what elevation, growing zone, and soil type you have? I'm not an expert but I've been growing them successfully for decades. You've mentioned a few things but I'll need the information to do what I can. I've grown them in a sandy clay as well as clay, and soils in between. I happen to use drip irrigation currently but flood irrigation is just as good. They seem to just want heat and water. Varieties do matter and in a hot environment I've found that Moon and Stars is probably one of the strongest varieties I've ever had, yet there are about a dozen others that I've used and do use to intermingle in my watermelon rows. I currently simply make rows and put them in the rows. They seem to do very well with spacing of 5 to 10 feet. I try not to crowd them with anything else. I suffer terribly from all sorts of critters that believe I'm running a food kitchen for them. Yes, animals love to eat the middle of my watermelons too. It's warfare in the garden :). I grew maybe 90-100 of them last year. I make juice out of them and refrigerate it and drink it all summer. Let's get to the bottom of the issue and get you growing watermelons!