Im a proud owner of a Bongo 1996 called borris

Got a few questions for the gurus out there..
When i put the back heaters on hot and the fan is turned on it smells like an old unused element heater not been turned on for months type of smell - a dusty weird smell .i know its had dogs in as u can still niff it under the air freshener now and then- and i found dog hair where the valet has missed- So is there a way to freshen it up>? is there a filter i can change or something i can do ?
it isn't a motor burning or rubber smell - at least it seems to work fine so doesn't suggest that . it smells like its hardly been used much for years ..
thanks guys!