I've been looking at caravan bedding options. I thought this was a neat idea, especially the matching doona - but I was looking for a low-cost solution.
As I view the link now it occurs to me that even if funds were available, the single bed size would swamp the 4WD mat that Vaughan prefers to use on his top bunk.
I started googling and learned the term inseparable sheets - hah! That's what I needed to make!
The linked tutorial gave instructions for joining the top sheet and fitted bottom sheet along the bottom edge. I wanted to join my sheets along the long (wall) side edge as well as the bottom, so needed to adapt the method.
At some stage Vaughan had spilled (or smeared) finger paint on the bottom sheet. I took the opportunity to cut away that section as part of the 32cm strip that was removed.
I halved the top sheet length-wise - thinking that I can possibly make three inseparable sheet sets from this and another pair of sheets (which will be next on the upcycling list). The original side hem was quite generous, so I unpicked that and sewed a narrower hem. I shortened the sheet by about 35cm, then overlocked the raw bottom and long side edges.
The tricky part was sewing the top sheet to the bottom fitted sheet. It would have been easier just to join the two along the bottom edge but I didn't want to do that! After some fiddling, I folded a hospital corner on the wall side. That gave a starting point to pin the rest of the top sheet along the bottom edge. (You can see the fitted sheet encourages a hospital corner on the non-wall side, also).
Once I'd sewn along the bottom edge and a little around the wall side corner, I gave up using pins and just sewed slowly - stretching the bottom sheet as I went and being very careful not to catch the elastic in the casing. I think I did OK. You can see the two sheets joined in the bottom collage pic. The joining seam is very narrow due to avoiding the elastic within the casing. Fingers crossed it will be sufficient to hold the two sheets together!