12v Constant DRAW

All these are good suggestions. Most TTs have a 12V kill switch to shut off when you aren't using the trailer. If you don't have one it's easy to install. But it sounds like you have a major draw if you are knocking down 2 fresh batteries overnight. Something is left on. As suggested, you gotta start looking, pulling fuses to isolate which circuit is on. Using a multi-meter is best but a simple 12V test light is good too. Someone mentioned the trailer brake breakaway switch being unplugged...that happened to me once long ago and it killed my batteries by the next morning.

I suggest that first you charge the battery up fully, then disconnect all the wires from one post and then see what has happened 24 hours later.

IF....the battery is still "full", then installing a true disconnect switch (or using the one that is already there) is probably the best solution because you should have one anyway.

If you somehow feel that you just MUST know what is doing the draining......then follow the other suggestions about meters and fuses.
But that likely isn't really necessary.

I am sure you checked this but once I left a l8ght on in my storage compartment and it took me 2 weeks of "battery" drain problems to find it.

several things will be a constant draw unless disconnected.
1) entertainment system. most in the "off" position are really "standby" and draw enough current to drain a single 12V battery in several days
2) CO and propane detectors hooked to 12V

these alone shouldn't drain the battery overnight. but, if the battery is drained, and you think your going to charge it in less than 12 hours with the common WFCO charger, well, nope, won't get near full charge in that short time. yes, it is supposed to put out 45-55A, but seldom will do so, usually gets stuck at 13.6V and 10A or less charge current.

In any case, to keep batteries from draining, you need to either
a) install a battery disconnect switch
b) remember to turn off or disconnect the things that are always on

BTW Some of my battery loads cannot be turned off per mfg design. A switch on the battery terminal solved that problem.

Remove all 12v fuses from the distribution panel;
Take a multi-meter and put in the mode where you can see if
a circuit is drawing a current (usually no more than 10A);
Test each fuse and find out which circuit is drawing the current.

Now trace back to the appliance; I had the same issue and it turned out
to be the smake/CO2 detector and the fridge (even if it was off);

My batteries would drain in < 2 days;

Also - good point about the break away switch

A DC clamp on ammeter is a very useful RV tool.

If your "camper" is a trailer, check that the emergency breakaway switch plug has not been pulled out. If it has, plug it back in (needs to be turned just right so it goes back in).

Make, model, and type of RV would really help zeroing in on your problem.

removes fuses from the distribution panel one at a time till the draw stops,

if that doesn't work, start removing wires at the battery one at a time.