Tony, you will not escape the condensation, unless you stop cooking and breathing. It is a very common occurence around the window trim and pop top aluminium framework in the roof. You can reduce it by ensuring good ventilation.
A dehumidifier would not work unless you closed all of the windows and put the top down as you would be trying to pull the moisture out of the outside air as well as that in the van.

Dehumidifiers do work in a home situation and very well. We were suffering very high levels in our new build bungalow, having to wipe windows down what seemed like hourly. We bought one of these https://www.johnlewis.com/meaco-arete-de...er-25l/p5375936 and now a light wipe on the very bottom of the windows in the morning, when we have had minus temps over night is all we need to do. We can also dry a full heavy cotton washing machine load in a few hours in an unheated room.

Colin