Chabad.org — English translation + Rashi
Torah Temimah: the Kehasim travel carrying the Mikdash (the holy vessels), and the Mishkan is erected by the time they arrive — the Gershonim and Merarim go ahead to set up.
English: “And the Kehasim set out, the bearers of the Mikdash, and they would erect the Mishkan by the time they came.”
Order of the march — carriers of the vessels travel after those who set up the structure.
The holy vessels never arrive to an empty site; the frame is ready.