If you don't have one then get yourself a clamp on ammeter. Blue Seas offers this one which can read down to 10mA. and seems to be a decent all round unit.
https://www.bluesea.com/products/8110/Mini_Clamp_Multimeter_-_AC_DC
Last year I bought a Klein CL 390 meter which is quite similar.
https://www.bluesea.com/products/8110/Mini_Clamp_Multimeter_-_AC_DC
Or borrow a friend with one of them and ask him to help or loan it to you.
Either one will tell you what the actual draw is when stuff is supposedly shut off.
I have been through this with parasitic draws although long enough ago that the draws were no where near where they can be these days but I still had to chase it down because my batteries were no where what they are now.
Many devices do NOT truly shut off unless the battery sw. or fuse/C.B. cuts off the power completely.
-VHF radios, stereo systems, radars, sounders, GPS's, inverters/chargers, USB chargers, a BMS . Almost any device where all you do is push and hold a button has some circuitry operational to sense that push. Not all but.
I am sure there are other devices that do not truly shut off unless you physically pull the fuse or trip the breaker.
Many of these devices won't draw much but a bunch of them together can actually pull quite a bit.
My 4 yr radar will draw 0.8aA with out a turn off sw. which I did.
But a decent ammeter can be a huge help.
There is another way and that is to use a DMM with a the ability to read DC current. THey are almost always limited to 10A but that should be enough.
Just disconnect the batteries, and shut off the loads. Then start reading fro draws. Of course you will still have to chase down all those items individually to find out which ones are still somewhat alive. Usually pulling fuses or tripping breakers.