Nice combination of the WPL truck and the Bruder Low Loader Crius,
The only work I found necessary on the trailer was to remove Bruders strange coupling arrangement and drill a hole forward of that mount and fit an M4 shroud headed bolt (Inverted) to act as a proper King Pin,
The 5th wheel was an easy fit on the truck after dropping the axle and sliding out the rear chassis brace then sliding the 5th wheel in place and drilling into the chassis rails to locate the 5th wheel base then simply re-assemble everything.