As a no deal Brexit or a non customs union Brexit is now highly likely, it is useful advice to look at what to do and what not to do.
There have been several instances of Swiss getting into trouble with German customs, either going to race tracks or to bike shows with exhibits.
https://www.bikeundbusiness.de/zollf...ring-a-764390/
This is in German, but it describes to Swiss bikers ending up paying customs charges of 3.200,- Euros on the bikes, plus a fine plus cost of persecution
pls note that the Swiss have an agreement with EU but it is more complicated that the British believe.
The fact that there are no checks at the Swiss / Eu border do not make smuggling legal it just means that one assumes responsibility when crossing it
It can make a difference if a car is road registered but this is be no means sure. Exhibitors at the Bodensee Bike Classic got fined and charged for road registered bikes that they had not declared on entry.
Having a Carnet ATA for each racecar makes life a lot easier and safer.
Failing that racing cars should better be declared on entry into EU after a non customs union Brexit. This can be done orally, but it having proof of declaration brings piece of mind
relevant law is: Artikel 136 Abs. 1 lit. b UZK-DA
personally I would be very very weary of crossing the EU border with non declared valuable goods, in fact I would not do that under any circumstances.
RuE