Hank should have been a little suspicious of Walt with the RV
The episode in Season 3 in which Hank rings Walt to ask about if he remember Jesse had a RV, and shortly after Jesse sprints out to his car and drives off in a hurry.
Hank follows Jesse who leads him to the suspected RV.
Jesse somehow gets Marie's phone number.
Even though Walt technically did not speak to Jesse, wouldn't Hank have been a little suspicious at least due to the timing of the events, and the fact somebody had his wife's number?
I guess at that stage he still thought Walt was the last guy to be meth cook.