There is a way to get into Watermill without exporting it (and without altering it and making it "Tree-less") AND without using Feral Heart + but its a very round-about way using map maker carefully. You simply make a map of your own, seperate from watermill. Include a gate/portal to "watermill" as the destination and if you do it correctly, (And I am not to be blamed if you do it wrong and I am not providing detailed instructions here) you can enter Watermill. You spawn in the corner of the map and can roam as you please, you just do not have a portal out. You have to homepoint.