Here is a relatively simple trailer for transporting 8 wide / Speed Champions scale cars. It has a spot for a winch but i decided to leave it out for simplicity. The wheel carrier can also be omitted if you dont want it, but this was originally built to tow a drift car so for me it was fitting and I like the feature. This is highly customisable and rigid. io file is provided if you want to make any modifications or adapt it to your parts collection.

It is 11 studs wide at the wheels and the platform is 9 studs wide so it will perfectly fit a speed champions car which is 9 wide at the wheels, they may scrape along the sides but this is the biggest i could do it without making it too wide. The cars should hold in place well thanks to the wells for the front wheels to sit in.