Updating Old Manpack

Hey guys and gals, I’m new to both the forum and radio world. I’m on several local fire departments in the area which went narrow-band a while back, and I was wondering, could I somehow wire up a new radio internally to an old manpack? We do a LOT of search and rescue, and with our area (Eastern Ky) our handhelds are difficult to use in suburban areas let alone rural areas, I was wondering if a mobile or base radio converted to a manpack would help with the difficulty of receiving and transmitting in the woods. All information is greatly appreciated!