Forming a contract-based HOA after most of the lots have been subdivided and sold

Does anyone know of any homeowners associations that enforce community rules contractually rather than through deed covenants?

I'm working with a resident association comprising homeowners and renters in a 91-lot manufactured home community. Former owners of the community sold individual lots to homeowners without enforceable deed covenants. Over half of the lots are now individually owned. The remainder are either vacant or are rented out to manufactured home owners. The residents created a membership non-profit a couple of years ago and acquired the non-individually owned lots last year. The RA would like to get everyone’s commitment to a set of community rules and regular maintenance fee payments. We explored creating a HOA, but not many lot owners are willing to subject their lot to a deed covenant. We are now looking for ways to take steps in that direction short of encumbering individual lots. Has anyone dealt with a similar situation?

1 - Good advice from NpS as usual & same state. NpS & RobertD24 : does Pennsylvania recognize claims derived from unjust enrichment aka equitable enrichment claims from the world of consumer protection & deadbeat partnerships ?

2 - What would motivate full plot 'owners' to voluntarily encumber their titles / onto titles to agree to run obligations that bind subsequent owners ?

Are there current or potential common services or an amenity that could add value ? ( a carrot instead of a stick ? )

3 - Could it be that the refuseniks are perfectly happy with the way things are ? ( I ask that because I live in a waterfront subdivision where the common ownership is bare tenancy-in-common with virtually zero governance mechanisms. There is no rule making power. Covenanted restrictions are negative and apply only to the privately owned lots. None includes an obligation to contribute the nominal contributions, but virtually everyone does. Voluntary association has never pursued the unjust enrichment remedy nor had much need. Works here since 1982. Wonder what's the problem where no built environment on the common waterfront except docks ? )