I’m really enjoying the game a lot so far, and I while understand that you are already working to resolve some of the issues with the trading post “ghost” storage, I do have a suggestion that I haven’t seen elsewhere for how to improve the trading post’s storage mechanics.
Instead of having to route all trading post goods through the building itself, you could have a static “work area” much like the market where all storage buildings within a certain radius have their inventory included in the trading post storage count. This way, villagers could still access the goods for other uses, and there would be a lot of goods immediately available for trading. It would be an intuitive way to make the trading post storage expandable without being unlimited. You could still have a quota for how many goods to have in those storage buildings, so that traders can be useful all year by helping to transport those goods from production buildings.
I realize there may be some technical requirements with counting items that the current trading storage mechanic doesn’t require solved, but looking forward to what you come up with!