My boathouse is nice, I built a big concrete wall with turret emplacements around it. It actually gets attacked quit a bit for me so it may be an ideal place because you'll be able to get more scrap from dead attackers.
I think Covenant would be a better small place because of how it is and plus traders show up there quite frequently.
(The build this guy is talking about is a STAY IN ONE PLACE build. You pick a settlement and you stay there... permanently. You don't leave to quest, you don't do nothing but build it up and stay there.)
I think my ideal place would either be the Kingsport Lighthouse, Because even though its a medium sized plot, you can actually build off of the top of the lighthouse. so Floating house. and plus you can build above the dock house behind it. If you place concrete around it, its a well defensible place. Raiders usually only come from the direction of the downed tractor trailer outside. You get a decent size house to put people in. Not many resources on site though. And the big problem could be the Children of the Atom you have to clear out, would be extremely difficult on a low level. Hell I was level 35 when I cleared it out and they gave me trouble.
I just don't think the STAY IN ONE PLACE builds are viable because of the lack of resources after a while. Sanctuary has a lot to begin with and as long as you can get some traders or stores it could last. Starlight Drive-In is good because of how big you can build it, but there isn't many resources there. You do have already existing structures you can house people in. I think the only way a StOP build could work is if you scrap all of sanctuary first, and then go to whatever place you're going to permanently stay at.