The easiest thing might be to persuade him to send a curtain sided trailer in the first place. Loading with a fork truck would then be easy. That is how I have moved my 6.00m in the past but I am careful with the trailer width and partially deflated the tubes so they donít rub.
If he wont then I would find a place with a yard ramp as Jetski and Chris have suggested see http://www.lantern.co.uk/yardramp_pics.htm
They are pretty common pieces of kit especially in places that load or unload containers.
If you use somewhere with a loading bay then you will have to get the rib on its trailer up into the warehouse in the first place which might be a problem.
If he is sending a box trailer then loading through the rear doors with a fork truck wonít be easy.