When the twins were very small, I rigged the single bed to act as a double cot for them, as they got bigger they switched to using the lower double bed.
However as they got older we had to separate them, to a bed each, or none of us would have got any sleep. The main drawback of this, was it left nowhere for Dot and I to sit, well not in any comfort anyway.
A couple of weeks ago, we all popped into a large caravan retailers and had a look inside a few motorhomes. The Twins really took to one of them and I told them we would buy it at the weekend, if we won the lottery (we didn't get it). However one of the things the girls liked about the van was, it had bunk beds. So I got to looking at our van to see how we could build bunk beds in.
I got the idea that I could use some of the bits from the cot I made for them as babies and construct another bunk above the single bed (bench seat). I made a design in my head and found all the bits I needed in the garage, then It took about two days to put it all together. I did have to go out and pay £3 for a length of wood just to strengthen it a bit but that was it. It is totally independent from the rest of the van (there is no damage to any part) and is removed to the over cab bed for travel and during the day.
We get a chance to try it out next weekend when we go away for three nights.