We have a Starcraft 235fb, which is an identical twin of the 22fb.
We used hanging cloth shelves, which work quite nicely. Even has one drawer in it.
It has a velcro top which wraps around and hangs from the existing clothes bar in the wardrobe. It is easy, you can put the shelf in whatever position you want, it fits the width of the wardrobe perfectly, and if the hanging shelves are too long, you can either cut the bottom shelf, or just let it collapse on itself at the bottom of the wardrobe (which is what we did). Easy to install, easy to remove, and doesn't add hardly any weight to the TT, like wood shelves would do.
I don't have a photo of ours, but it looks something like this, but is plain beige, not this weird zigzag stripe: