Mine is decorated all year round!
Because we either have overhead lights that look like an industrial factory, or nothing.
Our last van was an Elldis Aspire that had gorgeous lighting. Unfortunately bits kept falling off it, so we traded for something that would help us avoid involuntarily decapitating someone. But the lights are not, erm, ambient and atmospheric.
So, warm white LED fairy lights hooked over S hooks does the trick nicely.