You are losing 120vac it's dropping to a lower voltage due to the load of the space heaters.
Now the question is this a park side or an RV side issue?
On converter of the type I ***THINK*** you have the converter is normally connected (120 side) to one of those breakers directly No daisy chained devices
But if the actual converter is ... other than behind the fuse/breaker panels then it may be at the end of a Dasiy chain of outlets.
RV wiring is not really up to 1500 watt loads in my expierencem the Uni-box/Quick-Box outlets (Self contained) do not have enough contact area with the wires so they overheat and voltage is lost.
The CO alarm may have been responding to low voltage
or to vapor given off by overheated wireing (I've smelled that aroma when using space heaters)
I ended up installing special curcuits for my space heaters 12 ga wire and 15/20 amp outlets. but on your 30 amp rig that might not be possible