Does anyone know how hard it is to install these units?
This might help
its pretty easy, need at least 4 people to move it onto truck and then two people to fine tune the exact placement / seals when we moved mine i was inside it (with it closed) and therefore could use my legs to pick it up as my girlfriend sorted out the seal placement
some good info in this recent thread: How transfer a GFC? - Buying Used
Personally I met my seller at a Truck Topper place, they used their forklift and did the whole thing. I’m glad we went that route. Our transaction was more complicated because I traded him my shell + cash. One major upside to doing it yourself is that you can be super anal / specific / take a lot of time regarding the seal /shell interface.