For a conventional E350, it's not bad. You remove the finish panel only from the dash and remove the dog house. You have access through a heater core cover under the passenger side dash.
The trouble here is the ambulance prep package and what that means to you. Obviously all your accessories and ad-on's are in the way potentially. So, they may take a little extra effort to circumvent. But the good news is that there is that access box instead of removing the whole dash. Good luck!
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