I certainly wouldn’t wing it. There was a Welsh charity bike ride that got a van full of bikes impounded by the Spanish authorities iirc.
This was the original story
BBC News – Welsh charity cyclists in Spain get £7k bike customs charge
https://www.bbc.co.uk/news/uk-wales-62799594
I’m pretty sure there was a follow up and it was to do with carnets/paperwork. Basically van + big load of bikes was a red flag.
I know with people taking regatta trailers (multiple racing dinghies) to Europe there’s been some advice about ownership paperwork and also letters of authority to bringing friends boats etc while they flew.
Spares in retail packaging also were a red flag (the top sailors often carry spare major components if they’re not easy to source at the event).