Without going out to look at my van you wouldn't replace the mesh as the one fitted is part of your security door. There is a channel on the inside of the door where you can insert the plastic piping like a domestic fly screen and fit an extra layer of fine mesh on the inside of your door.
I actually found it relatively easy fitting it vertical. Seemed like it should be easier to start with the sides to get that tension right without bending the door, and then top and bottom with virtually no tension just to take out the folds. Makes a huge difference with the little bugs, particularly the midges.
Our van came with a white window mesh, which is now permanently stained northern dirt red. I replaced the lounge screen with a new one and thats the more traditional house screen grey. When I get some time Im going to have a shot at replacing the red stained kitchen mesh .... I'll post it up when I do.