Well, at the risk of looking stupid, here goes nuthin.
Ok, first up I will say, I am blaming the fact I was not well (feel better today though).
Last night I loaded the Cobra onto the trailer (all went well even though car is lower), So with handbrake on and in gear (Cobra), I drove the Valiant around and backed the trailer into the shed (all good)
I checked the balance of the trailer and all was ok, so I unhooked the tow hitch and drove the valiant out, all good.
Looking at the trailer I decided the Cobra needed to move forward about 6 inches, so I undid hand brake and knocked into neutral. Trouble started.
Well the Cobra started rolling backward, I tried to stop it, but no luck.
As the Cobra was rolling backward the front of the trailer came up, to the point where the back of the trailer was on the ground.
Cobra continued rolling off the trailer, until it wedged itself under the F 100, now I realise this sounds bad, but in all honesty, things could not have been better, only damage was a bit of the beige primer and it did break the locking latch on the LeMans filler (this is what stopped the Cobra going further under), if it had of been able to roll all the way off, then the trailer would have dropped, flicking the back up under the nose of the Cobra as the wheels rolled clear.
Now I did not get a picture at this stage (not sure if I wanted to relive it), but it was quiet a sight, to see the Cobra front wheels still on the trailer, the trailer nose way up in the air and the back of the Cobra wedged under the F truck.
After a long hard think, I decided to hand brake on and chock the Cobra wheels, push the F truck back to get Cobra out from under it, then chained the Trailer hitch to Bull bar on a Troop carrier I have, and backed the trailer and troopy out, all went well.
Here is the damage.
I can tell you it was not a nice feeling as the Cobra was rolling and trailer was going up.
I normally put my trolley jack under the back frame of the trailer when I unhitch it, dont know why I forgot last night?
So please be careful and secure your load properly.