Where to find the ground in a coach-built MH?

[Affinite]

I've started to fit a Victron B2B (non-isolated) in my Compass Avant Garde 194 and I'm going to position the charger towards the rear of the MH near the leisure battery box.
So far I've run in the feed from the start battery but Im a little stumped on how to find a decent chassis ground for the common negative.
Just wondered if anyone with a similar MH such as a Elddis Autoquest 194 had found a good ground in the habitation space.
I assume Im going to have to drill a hole through the floor to get to the chassis but thought Id ask before drilling
Thanks

 

[Two on Tour]

I've started to fit a Victron B2B (non-isolated) in my Compass Avant Garde 194 and I'm going to position the charger towards the rear of the MH near the leisure battery box.
So far I've run in the feed from the start battery but Im a little stumped on how to find a decent chassis ground for the common negative.
Just wondered if anyone with a similar MH such as a Elddis Autoquest 194 had found a good ground in the habitation space.
I assume Im going to have to drill a hole through the floor to get to the chassis but thought Id ask before drilling
Thanks

We have a 175, and I took my earth to one of the chassis to body mounting points by following the cabling the consumer unit exits through the floor to the underside of the van.
There was enough space here to squeeze to earth cable through. This I then connected to the hab battery negative and my B2B.

 

[Lenny HB]

Doesn't need to go to the chassis you can connect it to the negative of either starter or hab battery.
Mine is connected to my negative bus bar in the garage with all the electronics no where near either battery & it works perfectly.

 

[autorouter]

I'm going to position the charger towards the rear of the MH near the leisure battery box.
So far I've run in the feed from the start battery but Im a little stumped on how to find a decent chassis ground for the common negative.

The leisure battery will already have its negative terminal connected to the chassis by some method or other. It has to have its negative to the chassis in order to charge from the alternator, because the only alternator negative is the alternator body which is connected to the engine block, and from the engine block to the chassis.

In a coach-built motorhome it can be difficult to find a suitable chassis point, unlike in a PVC which is basically a metal box. So just use the negative leisure battery terminal as Lenny HB says.