Having camped in winter on two occasions in an insulated Designer. The only condensation issues were: 1)Under the bed 2)behind the side walls where it is not insulated. The under bed dampness wasn't really the same issue the second time without an electric blanket. The majority of condensation was in the single thickness sides behind the ply bed walls. Either a silvered foil or even Celotex may be suitable mediums against these solid walls. Also the condensation was observed in pretty cold weather.
My musings on forming an inner tent were made before I acquired an insulated Designer. In fact they were made before I went camping in November in my uninsulated 4 and found that a Tilly Lamp was all I needed to keep warm.
As you have no insulation other than the roof your issues will be centred on the front and back walls.
Erecting the awning lessens/stops the condensation on the front wall.
I see you have a head board a foot board can also be desirable. Instead of any condensation flowing down the wall and wicking into the duvet the footboard like the headboard keeps material away from the bedding.
Mikes solution works. You do have a condensation film on the PVC but it's separated by the waterproof insulation.
I had the idea of the silvered tent. As a cheap test I picked up an inner tent for a Conway [You must be registered and logged in to see this link.]
Click on 13 Conway Trailer Tent Sizes to find suitable candidates. I've not tried this yet. For me an inner tent would have both provided insulation and a modesty curtain. For those with insulated Dandys roof linings and modesty curtains are often used. A dandy does look a little spartan inside.
Questions about your Idea of a silk inner tent. I realise silk insulates. e.g. I use a silk helmet liner for my motorcycle helmet. What would be the cost of the silk? If there were still condensation and it drips would the silk absorb or would the moisture roll off? Not silk but man made fibres in tents are terrible for condensation. In a tent the difference between a nylon inner and a cotton inner is marked. Nylon forms condensation and is clammy, cotton allows much better breathability. Is that a feature of nylon or the size of the mesh formed upon weaving? Does silk breath well? Would it not just be too light. Compressibility is good but would the erected silk not just look like a wispy rag?