Insist that it's "a refinance with improvements" back at them, just to check their argument. Below is what needs to happen for you to comply with their wishes. The MH dealer doesn't actually need an "interim construction loan", they just need the land deeded over to them so that the permanent loan can be represented as a purchase.
The process of temporarily deeding a piece of land over to a builder for an interim construction loan involves providing temporary financing for the construction of a property. This interim construction loan is usually valid for 18 to 36 months and is settled once a long-term financing option, such as a permanent mortgage, is obtained