Melon is difficult to grow in our climates. I remember Monty Don trying out different planting locations on Gardeners' World, and the best (though far from brilliant) result was with deep raised beds (outdoors, but right next to his greenhouse) with masses of horse manure beneath the compost, and glass 'lids' which he could raise and lower to protect them from the weather. Growing them in the ground was a complete failure, and the greenhouse-raised plants were leggy and bore little fruit if I recall.

How are you growing yours?