Good paper is essential for pastel painting. The paper can be expensive though so try some experimenting watercolor paper. Use the best quality you can find. Nothing under 300gms and the paper must have some tooth to hold the pastel layers.
The thing is that paper on its own is difficult to look after when painting outdoors. Pastel smudges easily so transporting your masterpiece can be tricky. Then there is framing. The pastel cannot touch the glass which would usually mean that it must be framed with a matt board. This raises framing costs. There is also the thought that it would be nice to have your pastel painting looking similar to your oil painting.
The solution is to make a pastel painting panel by sticking the paper onto a panel. I use 3mm MDF. I suggest stretching watercolor paper first. Once dried stick it onto the panel as described in the video below. Tone the paper with watercolor as you wish and use the panel as you would regular painting panels.
The panel fits into a wet painting carrier so it is safe when transporting. The panel can be framed without a matt board too. What about the glass I hear you say? Simply use a small plastic spacer on the edge of the glass so that the panel does not touch the glass. I use tiny adhesive silicone widgets that you can get a hardware stores. These widgets are normally used to glue under heavy items that may scratch table tops.
The main thing is to make your pastel painting easier and give you the opportunity to use pastel en plein air. The framing benefit also improves the impact that your pastel painting deserves.