What I love about tax work

You learn something new every day!

Sounds like this is a mobile home in a co-op.  I always think of co-ops as something found mostly in New York City and other foreign countries. 

But apparently there is a movement to convert trailer -- excuse me, mobile home -- parks into co-ops.

And that's what it sounds like you have here.  

So I think the stepped-up basis rules apply, but I really don't have any experience with co-op ownership.  There are a few old ones in my area, and I do know that one of the major drawbacks is that they are bought and sold for cash only -- no financing.

For more information see  https://rocusa.org/   -- they might even have some tax information.