I'm not sure which kit you're talking about, but I went with the Sport Seat II kit from TMI (foam and upholstery - sold separately). I'm 6'5" and 300-ish, and have no issues with the extra bolstering provided by the Sport Seat II set.
As for tips/tricks:
- Get more hog rings than you think you'll need
- Get the 'bent' hog ring pliers
- Use really thick wire hangers as listing rods if some of yours are damaged (they work in a pinch)
- Use plastic bags on the foam to help the upholstery slide better
- Place the cover(s) in the sun before installing them (they'll be a bit more pliable)
Mine turned out decent enough - the creases relaxed after a bit (especially with my chunky ass getting in and out of the car)
My driver seat - frame was rotted out, so I used another from a parts car:
Here's how they came out - like I said, the creased relaxed a bit after some more tugging, time in the sun, and actual use:
You can see how much thicker the Sport Seat IIs are than the stock 'flat' buckets.
I also didn't reinstall the seat 'bumpers' (plastic thingies that buffer the seat back against the seat bottom), which made them lay back a bit more, so I have just enough headroom. If the seats fail for whatever reason, I'll order a set of the TMI Precision Seats with the same upholstery already installed.
I have a whole new appreciation for those who do upholstery, that's for sure.