[page=How to do it!]
To make a custom car, you need to firstly spawn a Prop, and a Vehicle - for instance, a Bath and the Jeep. Secondly, we need to make them non-solid by shooting them with the the NoCollide tool.
Now, place the prop in line with the vehicle. Make sure that its placed under the seat (see screenshot), and then freeze the prop.
Then weld it together. Now go to color and draw all the buttons down so the color is white with gray stripes like on the picture. Now weld the Vehicle and Prop together using the Weld Tool.
The final step is to make the Vehicle invisible. In the Color section of the tools, set all the Color properties to 0 so you get a white image with gray stripes. This makes the object invisible.
As a result, the vehicle is made invisible, and only the Bath remains. Because the two were welded together, you can enter the vehicle but it looks like you are actually driving a Bath. Remember to unfreeze the Prop before you attempt to drive it.
The invisibility idea can also be applied to just the car itself. Making it invisible then entering it will make you look like you're sitting in mid-air and driving.