I use hot water and push the connection together to break the seal before pulling it apart which seems to help a lot since the tubing wants to contract if pull first.
I've done it using a power strip for 10 gallon batches in two different carboys. Seemed to work fine. Watched the fermometer on both carboys and they stayed at the same temps.
If you are talking about the 20g megapot from NB. I have that exact same setup, and it fits perfectly with no modifications. My brewpot actually measure 20.5" at the top where the lip is roller outward. It tapers in a little on the bottom.