I have a 1950 1/2 ton PU and want to install the cab roof liner. What is the best way to do so?

It has a floating support.

Do I place the two liner pieces into the floating support and then fit it in? Do I put the rear piece in first and then the front?

Before I start manipulating the somewhat fragile pieces of cardboard, I would like to know how you guys did it.

Thanks.