Installation help; two parallel main panels

300 amp service.
At top of meeter there is a split for 2 panels.
Nowhere to put a single clamp to capture the entire leg.
I had to do it pre meeter.

I have an always on of 400w even when I shut of 99% of my breaker. The only breaker I left on was the one for the sense monitor. It shares a breaker with a lighting surge protector.
I plan to disco the surge protector and check back.

If it is still there. How can I subtract the 400?