IF Tiffin was using the current Nippon Denso AC units in 2007(It must have the dash controls in the linked pic), it is outside on the Evap housing. Current Tiffins use the Denso AC system. Look at the white object in the pic on this link. That is the cabin filter. Doug Older Denso systems do not have the cabin filter densoheavyduty.com/hvac-systems
It is smart to install a cabin air filter on a MH why most RV mfgs don't is beyond me. I'm not able to get up under the intake area in fron of the coach or I might figure out how to make a housing with an easily changed air filter. I now I have mentioned this to American Coach several times but not lately.