I agree with David in that you always need to have circuit protection on the main B+ trunk line right off the battery. As he pointed out, in many cases, a fused distro block next to the amps can be redundant and are not always needed. So just going with a pair of non-fused blocks, sometimes called Ground Blocks, is all that needed.

For those installs where we want to add a little bling or flare, we may use that fused block w/meter. Or, for a less expensive option, there are a handful of simple 12V digital voltmeters out there. Flush-mount one to your amp board or at the helm. If your helm has an analog volt meter, you can use it to monitor both battery banks by using a SPDT switch.