As I explained already in the main post, things do balance themselves out assuming everything is watercooled and dumping heat into that attic room. I was using this setup for 2 years already with 6900K/2080Ti SLI and everything was always within safe margins, the room was never below 8-10C and dew point inside the case was below 5C because the main room is temperature and humidity controlled with AC and there were no major heat sources within the case. But now the temporary situation is that I do not have GPU waterblock yet, so not only I am not heating the attic room up with GPU heat, but heating up main room instead, so everything went completely out of balance. It will be fine once the GPU block is in, temp within the case will go back to 19-21C, so dew point will go back to 5-7C, and attic room temp will go back to ~8-10C at the worst, so water will be like 11C idle.It sounds like the issue was leaving the MO-RA in that unheated attic. Which means it's bound to get worse as outside temps stay subzero for extended periods of time.
You should look into insulating the tubing that travels to the MO-RA if you want to be safe over the long term.
Even in the worst case scenario like this one I was only a few degrees off, just lowering the case temp by 2C and increasing attic temp by 2C would avoid the problem.
Having it like this during winter is great as it is basically a free water chiller, but one condition is that the heat from PC has to be dumped into radiator room to maintain good temperatures there, which cannot be done without GPU block. I have to wait till 22/12 for delivery so I will have to actively heat that room up temporarily.