Why do you think you ‘see’ everything the FBI is doing?
They had already investigated the camper.
They may have gone in today because they were looking for new scent material for the dogs, and the parents told them of something in there.
Depending on evidence available at the time, the first search warrant may have been very limited in scope, i.e., electronic communications devices. New evidence/probable cause may have allowed for an expanded scope in a subsequent warrant.
What date did the FBI originally investigate the camper? What is your source reference?
The media, with many camera angles, have been camped outside the Laundrie home non-stop for weeks. The media have had cameras trained on the Laundrie property since before the FBI was involved. The camper has not moved since the FBI became involved in the case.