I don't know if this feature is already present on the mod (and i just got some issue that made it not work), but i really think that could be an option if not yet on CarryOn.

Basically, when trying to place a entity or valid placeable inside boat/minecart block, CarryOn should place the thing "inside" the boat/minecart. Conversely, when trying to pick a boat/minecart with a carryable block/entity inside it, the mod would first remove the block/entity inside the boat/minecart instead of remove the bloat/minecart and drop all items (if its a chest)/leave the entity on foot (that was the behavior on 1.12.2).

Any updates about this?

It is a feature that has been requested a lot but I've chosen deliberately not to implement it so far, but I might change my mind at some point.