Sorry George. Always sown in pots first. It takes longer for them to settle but I feed them well. Horse manure the previous autumn, then BF & B late spring and through the growing season. make a pocket, water well, dollop of rotted horse manure, then soil, then plant . water again. I plant an old 4 litre milk bottle with the bottom cut off upside down beside the plant. Stick a cane in it ( it gives an idea where the plant base is when the site is covered in runners) I water/liquid feed in this. keep an eye on the plants. give Epsom salts a couple of times in the season scattered round the base. Potash/Nitrogen liquid feed. Water most days, amount depends on how dry its been. I've always found that this gives us a good squash/pumpkin harvest. Some years better than others.
With regard of your plants dying: I've had this occasionally. Not lost ALL my plants though. one or two were obviously slugs, but some just seemed to wither away. I've had Brassicas do it - not club root related. No idea of the cause but suspect something in the soil. Fusaria? Ants even? I HAVE lost all my sunflowers at home this year. Again, one or two to slugs but the rest just withered away - also a few night scented stocks that I'd grown in a large tub. Just wilt and collapse
Hope you get some produce. I'd try just picking your site on prepared ground, plat at usual depth, liquid feed. I've pot grown courgette and planted out late July with good results. cropping int October. Our sie is in North Warwicks. Best of Luck George.x