Another one from an old magazine article. This design is for a basic folded half-wave vertical for the 11m CB band on 27MHz but it can also be adapted very easily for 28Mhz or 29Mhz. For 10m operation, try reducing the half wave section to 5.10 metres and the quarter wave section to 2.53 metres.
It really is a case of experimenting and see how you get on. It's likely the biggest challenge will be the mechanical construction rather than adjusting the VSWR.
One particular advantage of this antenna is that the quarter wave tuning section effectively puts the radiating element higher above ground level. This fact alone can have a significant effect on the performance of the antenna as it begins to get clear of buildings, electricity wires and other clutter near ground level.
A lot of novice CBer's get fixated on 'advertised gain' and different types of antennas whereas they should be concentrating on getting a decent antenna up as high as possible.
While the Slim Jim won't be as good as say a Yagi beam up on a tower, it should still perform pretty well.