HO scale model maker A Class will be releasing plastic body kits for the JNR 80 series "Shonan densha" sometime this spring. Both unpainted and painted body shells will be offered. You will have to purchase bogies, underfloor details and motors separately. A Class suggests Nikko Models bogies and underfloor details for these.
So far details are sketchy, here is the info provided by A Class (click on the picture):
http://www.dcraft.co.jp/aclass/a_top.html
Example of a Nikko bogie that can be used for trailer cars (TR48 type):
http://shopping.hobidas.com/shop/rail-hobidas/item/NKM-0036.html