We have a convertible 1970's VW Beetle that we'd like to take around town. However, it's a convertible, and it only has lap belts in the back. As such, we don't feel comfortable putting our six year old, in her booster seat, in the back seat. There's no shoulder strap, and of course, no roof. Ideally, I'd like a 5-point harness that works with a kid's booster seat... But do any of you have any ideas that might work? The alternative is not to take her around town in this car, which is fine; but if we can find a way to secure her, that'd be great. Thanks.