Bad luck Annie, this is a hard one to solve.
Are you sure they are wireworm, i.e. orange brown, about an inch long, like slow moving centipedes?
Was your tunnel put up over grass, which is where wireworm mostly live? If that is the case it may take longer to resolve as they are well established, with no know remedy except time, at least a year. Even chemical gardeners have no effective pesticides.
Or might they have come in with imported topsoil? In which case raking through it may enable you to find and remove them?
As far as I know they do eat tomato roots but hope I am wrong… does anybody else have experience of dealing with this?