I don’t know where you live, but where I live it’s extremely rare for a cul-de-sac not to have a center island; including curb and gutter, grass, and landscaping. Additionally, nothing in the OP’s post said he was worried about the outside radius of the cul-de-sac. Furthermore, he talked about the length of the trailer, which would only be a factor if he was worried about the trailer tire path.
Your assumption is the outside radius is the problem, mine is that the inside radius is the problem. So until there is clarification ….