Sowing vine fruit indoors

Blue Onion

I will be sowing my pumpkins, watermelon, vining courgets, and cucumbers within the next week or so.  Typically I plant them in 3 inch pots with seed compost, then pot on a few times before they get hardened off.  They always seem to sulk, die, etc. with each potting on, loosing over 50% of the plants typically.  Do you suppose I could just sow them in well draining garden compost in a slightly larger pot, and skip all the potting on?  I'm about four weeks from planting out, so three weeks until I harden them off.