I know were your coming from i have the Quicksilver HD430.
What i will say is i made my own launch trailer as i use a touring caravan too.
Have a look here
Testing water for my Quicksilver HD430
All told it took me about 5 hours to cut and weld,The steel was free from work
.The wheels were £45 and i still need to have it galvenized yet.
I was forced in to building my own though as i couldnt find a folding one for the 4.3m long.I estimate that its cost around £140 to make not inc my labour.
If i could have though i would have just bought one.