Basically, the answer to your question is no. Remember content is king. Search engines determine relevancy (in general) not just by reading the meta tags, (if they did there would be 200,000,000 pages coming up under"sex") but by comparing the tags with your text.
Doorway pages in my opinion are for the purpose of supplying more specific info about a particular subject that relates to your main page. Your inflatable boat site is a perfect example. If you'll change your title, description, meta tags AND TEXT to actually talk about "whitewater rafting" then put buttons or links on that page intended to sell them inflatable boats, now you will probably place high under "whitewater rafting" and sell boats at the same time and you don't have to worry about a search engine or anybody else getting mad at you.