Here is one article on servicing an RV fridge. I just skimmed it but it looks good:
The orifice is part of the burner assembly, at the bottom of the chimney. One screw will allow you to remove the wind deflector, then another will allow you to pull the assembly - gently - away from the wall. You don't want to bend the long tube it is attached to (the fuel supply) but it will give a little so you can get to it easier. Then you remove the rectangular mixer, it will unscrew from the long tube. Careful here because the orifice is just sitting on the end of that tube. It is a very thin piece of aluminum no bigger than the top of an eraser.
Going by memory here, it has been a year since I've done that.