That's for goods trailers, as in HGV semi and full trailers.
You could fill it in and see what they actually do with it. Demand a paper trail.
I have filled it in & sent it off. The first thought of the person who had it passed to him at VOSA was that it was a wind-up. He was new to that section and this was his first case. Decided to call their bluff, by phoning the number that was given & asking for the person named on it(the only details missing on the form as given here). Me.
Response by me was that it was a genuine appliction, brought about by a request made of me, by my local council. Who I named to him.
Also given was the manufacturer of the trailers in question, bikes at work. And a short decription of what a Brox was. He'd never heard of one up until he saw the form. Which further fuelled his feeling that the application was a windup.
Informed, that they(VOSA) would not have to check the trailers prior to use & that whilst the form was meant for powered vehicles, if I wished to go down that road I'd have to get the Brox tested under the SVA. Hence me driving the DVLA in Leeds nuts trying to tax it.