anyone built a trailer crane?

[Kwill]

Im thinking about building a truck crane to put on my 16 ft trailer. I go to alot of auctions and buy junk and heavy stuff and sometimes they dont have anyway to load. I looked at  the harbor freight ones and i just dont see 150 dollars. Anyone built one like these? I want to mount it on my trailer where it is easily removed while going down the road. Im going to install a electric winch on it. I will also use it to load my cedar logs at times. Just looking for some ideas if anyone has built one. 

[Don P]

On the tongue near the jack or over the axle would be best. A friend put one at the back of his pretty light trailer and bent the frame when he lifted too heavy a load and forgot to block under it.

[Riwaka]

uk trailer crane, but need a defense department budget to make or purchase.
leg supports etc
SwingLift Trailer Mounted Cranes | Penny Hydraulics   (UK)