I've never had replace a blind on 400x400. My 400x400 in the shower and washroom come off with a gentle pull. 2004 coachman pastiche. The net is just a pull off. No blind.
Sounds like the “skylights” we had in our previous AS Clubman MH. We replaced fly screens & blinds. From memory (it was years ago), the frame with blind & screen just popped / prized off the cassette, the new one snapped into place.
Job done,all 4 skylight cassettes removed( they were filthy) thorough gentle clean and all refitted.They look like new. Best tool a car trim removal spanner. Only1 trim slightly damaged and fixed with very small cable tie. Would recommend this task on older vans mine is 2012.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.