Inappropriate clothing isn’t linked to the season you use your van in anyway, style aside, my usual socks and slides apparel footwear is equally inappropriate for night trips to the toilet blocks through wet grass in the summer as it is in the winter. The difference is I can justify turning the heater on in winter to dry them quickly.
We do go away less in winter but that’s mainly to do with the limitation of holiday days, May as well use them in spring/summer/autumn when the weather is a little better for outside activities