Can this unit be installed in a crawl space where my well unit is located?

it needs a vertical space of about 55 inches

The unit stands 47 and 7/8 inches high . How tall is your crawl space ? Dirt or Concrete ? If you have the head clearance and you have access to a power supply ( we'll presume you do with a well unit ) and Access to your water supply for the house both in & out and somewhere to drain the brine water when the unit cycles then i would yes to an install . But if its like most crawl spaces under homes ... I believe the unit would be to tall to place it there. If you have access near your water inlet inside the house like in a laundry room or garage that might be a better placement of a unit. I have mine sitting on a concrete Pad outside directly next to my Laundry room, I installed a electrical plug with a GFI and dug a hole to accommodate a 5 gallon pail. I drilled holes in the bottom and sides of the Pail then placed it completely down into the hole. I filled the pail with a fabric screen on the bottom and poured rock and pebbles to fill it up 3/4's of the way. I place the lid back on the pail and drilled a hole in the lid to accommodate the green drainage hose allowing the brine water to drain into the bucket. By Doing thisI essential made a mini Septic tank . The Lid to the bucket remains flush with the ground. I installed it over 12 years ago and its still draining . You could consider placing it out side providing you live in a climate area that doesn't freeze for long periods . I live mid-state in Florida .

Sure. As long as you have the space above the unit to pour in the salt and service the valve. It doesn't freeze down there, does it?

Look at the height and service clearance.

Not unless you have a very large crawl space and are willing to crawl back there to put salt in it. It is about 4 ft tall and must stand vertically. It is not designed for any outside exposure.