Potting on squash seedlings

I've probably gone a bit early with my first squash seedlings - they're already getting their first true leaves - and my plot neighbours have said that as our site is on the fen just out of town it's very likely to catch any late frosts. I was thinking I'd put my seedlings into quite large pots as they will probably grow a lot in the next few weeks. Would you add a bit of rotted manure when potting on, or is that not necessary at this stage?

I planted my BNS a bit early last year so rather than put them on the plot and risk frost I put them in the GH in larger pots and they shot ahead so in late May when I put them in the open ground they were well ahead.