Would it be ok to just use that no nails stuff do you think to stick them together ???
don't worry what people say,its only when you start putting shelves on the outside of the van that you may need to have a chat with someone
stick what together?
I can see one immediate challenge...that piece of wood if it is just resting on the existing worktop and just resting on a ledge on the other side may slide sideways and drop everything on the floor especially if you are setting something on it quickly....a piece of gripmat under the wood on the kitchen side and a thin piece glued to the ledge or batten on the other would probably do away with this risk.
I have an oven I don't really use because they dont get hot as a domestic oven. I keep pans etc in it (and shoes in the bottom bit! It doesn't get hot even when oven used).
The oven doors make good temporary shelves!
I have a metal desk at home with 2 slide out shelves, really useful and take up negligible space retracted, but it's beyond my woodwork skills in my MH