Вот копия ответа финской таможни на мой дополнительный запрос:
From: Heino-Värri Ritva [mailto:**@tulli.fi]
Subject: VS: TULLI_EMAIL_NEUVONTA
The restrictions is not concerning the temporary import.
You can bring your motor boat on trailer to Finland for your vacation.
At the Finnish border you have to stop for declare the boat and trailer to the proceeding of temporary import. Customs officer can demand to fill some form of termporary importation.
Ritva Heino-Värri (e-mail:***@tulli.fi)
Tullihallitus - Tullstyrelsen - National Board of Customs
Answers provided by e-mail are a part of the general information services of Finnish Customs and are not binding. The National Board of Customs may, upon application, issue chargeable binding advance rulings on the application of the Value Added Tax Act, the Excise tax Act, the Act on Fairway Dues and the Car Tax Act, but not, however, on taxation values according to the Car Tax Act. Binding tariff information and binding origin information are normally free of charge.
То есть ограничения не действуют на временный ввоз.