mobile showroom; display van; retail truck
A vehicle fitted with facilities for displaying or selling goods, often used for promotional tours or temporary retail.
wasei-eigo (Japanese-coined English), from caravan car
A mobile showroom toured the country to introduce the new product.
I heard you can even try on clothes inside that display van.
Wasei-eigo from English 'caravan' + 'car'. The term is not used in English with this meaning.