Thank you Gigith, those videos should help loads, and the explanation was very good. One typo though, you called the item you're merging the...
I doubt this would work with vehicles, seeing as they can get destroyed by boxes hitting them, but it's worth a try I suppose.
I would suggest using another fence box as a pusher, that way it's the same size.
To merge into walls is the same process, but at a 90 degree angle? I'm not sure I quite understand that... Could you be a bit more detailed please?