Winter windowland

Yes close all blinds & curtains condensation is warm air on a cold surface hence the more insulation between warm air & cold windows the better.

i have never closed my blinds the winter sun gives a little heat in the van and the air can circulate freely around van

By using a low wattage heater ie 55w to 100w the temp inside the van is only kept a few degrees above freezing. 5 deg to 8 deg is the perfect temp as moisture traps and dehumidifiers don't work below 5 deg also below 5 deg moisture bags just fill up in no time as all the air is damp.
Also fit winter fridge vents and ensure as much air from the outside is prevented from getting into the van.
BY not causing a wide temperature swing inside the camper ie high wattage heaters this does away with condensation when coupled with and external screen on the front and blinds and curtains pulled. Handy also to leave all internal doors open cupboards etc
Wide temp swings or campers just left over winter with nothing do the most damage.

Everyone has their own view on this subject all I can say is we have no condensation and no swelling of joints , panels etc so it works in our case.

I bought a roll of silver insulation that's used in houses and cut a piece in the shape of each window. It works super. I've been told that its not good to have the blinds down for a prolonged period of time.

Robbie I cut it the size of the window, doubled it up and used Tuff tape to join it together. That makes it strong enough to sit in the window just behind where the blind comes up. Hope this is helpful. I use them all year round - great insulation in the winter and great to protect the interior from the sun in the summer. It took me just a few hours to make them.