Rescue Apparatus: Walk-in vs. Non-Walk-In?

My department is considering combining a hazmat unit and a rescue company into one vehicle.  Both of these companies are currently cross-staffed with either a quint or an engine company from two different firehouses.  This could change down the road, and hopefully, will become a staffed unit.

Our current hazmat was a demo unit bought when our jurisdiction was growing extremely fast and we needed the rig and was initially put in-service as a rescue.  It was converted to a hazmat unit when our rescue equipment was out-growing the rig's storage space and we obtained a Hackney straight chassis beer truck from a brewery.  The Hackney beer truck was turned into a rescue company with two compartments containing MCI equipment for forty patients.  Both these trucks are old, are worn out and aren't terribly well designed for what we are using them for.

I'd love to hear some thoughts on walk-in vs. non-walk-in style rigs and what you all think the pros and cons of both are.

Thanks for your time and thoughts!