Lotech,
I beleive the best way to bring people to Christ is to live in such a way that people want to know what makes you so happy...what makes you such a kind, caring, and thoughtful person. I think that a more subtle approach (at least to the tent design) is best.
Instead of making your tent a "billboard for Christ" why not paint that Christian fish symbol (not too large) on the side of your tent where it can be seen by passers-by. Also, a sign that says "Angler's Welcome" might invite others in. This way, you've sent a clear message about your faith, but you've not whacked us over the head with it. You've also extended a kind invitation to those passing by.
I would not attempt to preach the gospel to your guests, simply show them Christian warmth and friendship. Be kind, and thoughtful, and offer your guests coffee, hot chocolate, a snack, a beer (I don't believe it's a sin to have a "drink"), or whatever. Talk about things other than Christ and faith(you are presenting a model of Christian life to your guest, not preaching to him/her). When your guest goes to leave, thank them for sitting with you and let them know you have a gift for them. Present them with a bible and wish them the best of luck with their fishing. If they take the Bible, great! If they don't, don't force the issue. People are called to Christ, and today might not be the day they hear that call...it may come days, weeks, or years later, but your actions will have been a part of that call to Christ.
I'm probably the type of person you'd like to have at your camp fire (I was raised in the church, but left it many years ago). If, as a passer-by, I saw the tent you described, I would immediately classify you as a religious nut, and pass by without stopping.
If your aim is to bring people to Christ, keep it simple (as Christ did).
