45 Degree Firestop Spacer. Use to go through a wall. Or, possibly where a window is in an RV if that is how you are installing. If you decide to go through a wall, then be very careful. If you make that decision, elbows always slow down your draft. However, it may be your only option. Thru-wall installations are tricky. You must be careful. Furthermore, you must plan ahead to make sure it is safe. Do you have a thin wall on an RV. A lot safer than out the wall of a shed home.
45 Degree Installation
You really should only go out a wall that you can go through safely at a 45 without any other things in the wall that can catch fire. For instance, an RV wall is thinner, normally has foam style insulation. You can cut a 10" hole. Then line with metal. This will give you an air barrier. You need this around the pipe. Use HT UL Rated pipe only. Never single wall pipe.
Use of this part is paramount if you are going through at a 90 degree angle. https://flameinnovation.com/product/4-wall-radiation-shield/
You also need to use the HT UL Rated pipe through the wall. For instance, as you turn away from vertical. Use a 45 elbow paired with another to make 90.
Parts description pages
https://www.selkirkcorp.com/en/ Find and read about your parts a little more here so you can make a decision on your install.