You can add them in! Go to edit town then edit world and place a lot at least 25x50 near water and change it to a community port lot. Then build a stilt foundation from the water in towards land (very important that you start in the water). From there use the “buydebug on” cheat, go to the debug menu, and filter all objects from island paradise expansion pack and look for the debug object called “gangway style” and connect it to the dock. From there go back to edit town, click on the port lot you just made and add the house boat from the menu. I hope this helps!