Firstly look in the warmer places...
Secondly look under cupboards, beds etc, in the tightest little nooks and cranmnies,
One of my JCP's has escaped a couple of times, through the tiniest little opening I had left in the glass doors, still to this day I don't know how. I opened it a tiny bit only to let in a little more air as it was extremely hot.
The first time my son found it snuggled in his fluffy toys on top of his bookshelf.
Second time, she was under a chest of drawers, I removed all the drawers and found her in a dark corner.
Third time she had managed to squeeze through a tiny crack in the fake rock wall in her enclosure, I had to pull the enclosure apart to get her out.
Good luck, a snake that big will turn up ....somewhere!
Cheers