My Contest Suggestion
How about a combination scavenger hunt/puzzle/trivia challenge? Start with a clue, have an image/link hidden somewhere on the site that the clue will lead to. Clicking on the link would bring up either a trivia question, puzzle, riddle, etc. Completing that challenge would give the next clue. A few examples I can think of would be to have a riddle that the answer would point to a specific tank design available on the site, the page for which would have the link for the next clue, or vaping related trivia questions that could range from having to search some of the news/politics threads on ECF for the answers, more technical things like calculating nic content of a combination of different amounts and strength juices. There's a ton of options you'd have with how long and difficult it would be, what kind of challenges you use, and I think it'd be both fun and would allow for plenty of opportunities to showcase your products through the contest.
Edit: Doh! Shows what I get for spending too long typing that out.