On-site properties?

Just like to know in further detail what these properties are, and how they are different from normal properties. Far as I know, these are the relocatable homes. Advantages/disadvantages of buying these types of dwellings?

I’m pretty intereted in one of these houses that I’ve found, so I’d like to get as much info as possible before I jump in. Should be calling the vendor tomorrow morning. Also, why is there no stamp duty on these dwellings? Thanx![]