Without seeing the details of the deal you and your platonic co-tenant made to buy it,
I can't say for certain, but...
On the assumption that you bought the building "outright" (so to speak), and
so far as the building itself* is concerned, you are not involved in any kind of
deposit/ loan/ lease/ tenancy/ licence/ whatever with the park operator,**
then for testamentary purposes, I don't see how building is anything other than legally akin to a caravan, a car, a boat.***
This means, among other things, that the principles on joint tenancy do not apply the way that they do land.
In which case you should make arrangements in your will(s) for what happens to your share(s).
This is a job for a solicitor.
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* That is, not the land lease
** Such as one might be in when living in a bricks and mortar retirement village
*** For example, it's yours to put on a truck and take elsewhere at any time.