trailer-made-scratch becomes boneified tool

[Frank S]

What is the reason for 2 cranes rather than one? I am thinking of mounting a crane on my F150, probably on the passenger side bumper. Anybody done this?
Rob

Unless you build your own bumper it is a bad idea. A great idea if you construct a substantial bumper and add a drop down support leg. A lot of people mount them in the beds at the rear corner again this only works out well if real steel is used as a base plate on the floor and it tied underneath to the frame with additional support brackets.
I made my trailer strong enough to accept these cranes with them in mind while I was building it.
To answer your question as to why 2 of them. this gives me the option to load from either side of the trailer without having to move it also 2 cranes together can lift 3000 lbs I have used them to lift those totes full of water as well as to load lathes and mills by working them in tandem and using a 2 part line and connecting them to the center ring of a 2 or 4 hook sling it gives me a safety factor that I wouldn't have if having to do the lift with only 1 crane.
When I say substantial bumper I am talking about something along the lines of 6x6 x3/16" square tubing welded directly to the frame with gussets. even then the bumper can be torn free of the frame.