Yup, 5 mins on a 155, it's in the passenger footwell, kinda behind the glovebox.
Misting will be the damp interior you've got.
Dampness will be one of.....
blocked drain holes (two under the scuttle panel, centre and passenger side)
a leaky heater tap (apparantly easy job and cheap)
matrix (not very common)
door seal (bugger to trace, try talc)
leaking window/screen (bigger bugger to trace, try hosepipe)
wet feet (easy to check, shouldn't do it in summer unless you live in a lake!)
That's the order I'd check too