I've had an SV-24 for 4 years now...check that, 5 years...received as a Father's Day gift my wife and kids, and it was set-up and ready to season when I first laid my eyes on it, so I lack the benefit of having assembled it myself, but that's a minor drawback. It has been my main smoker for several years, handling most of the meats for all of my larger gatherings (6 butts, 8 yard birds or 3 briskets per smoke) and smaller meals alike. I'm leaning more towards the dark side again recently, wanting to grab a small
WSM for my smaller household now (the kids have almost all grown their wing feathers flown from the nest), but I won't give up my Vault...it's been too dependable for bigger projects.
As for lack of seal around the door, be sure it's level and the legs are spread evenly so the cabinet has no twists and is plumb. If the door doesn't seal very well at all you can eye-ball the edges to check for warpage and adjustments can be made by just carefully twisting the door in the direction it needs to be, either top or bottom, on the latch side.
The only mods I've done are bending tabs on the side intake louvers so that I can fully close the intakes. I get lower grate temp variations with an added 24" stack on exhaust which is just sitting on top of the cabinet. It's a tapered stack from a round outdoor wood fireplace that's about 6" diameter on bottom and 4" on top, with a rain cap. The stack increases the overall draft through the cabinet, and in combination with having the intakes closed, it seems improve top to bottom and side to side temp variances quite a bit. I really haven't found much need for additional mods to the SV-24 to improve performance, but I'm sure someone has done a few other mods. Mine just seemed to need a little coaxing, but overall, it worked quite well in the stock configuration, until I started loading it up with large amounts of meats.
For smoke woods, I use chips for a faster onset of smoke, and chunks of various sizes to extend the smoke duration. Size and amount of chunks depends on the length of time want smoke, of course. The larger the wood the longer and slower it will smoke, and the more wood the heavier the smoke.
As with all vertical smokers, be aware that larger objects in the smoker will baffle the heat to items above it, especially if in close proximity, so when using large pans or smoking large cuts of meat such as whole brisket you need to place the larger items above everything else, or, rotate grate positions and at times I will run a bit higher chamber temps to compensate for the baffling effect. This is also true if you load up several grates with ribs...grate rotations from top, center and bottom, as well as front to back (280* rotation of the grate) will help even out the cooking of items on each of the different grates. Oh, and don't get any food too close to the cabinet walls or door...these are hot spots that will overcook your goodies, and at times, scorch them beyond recognition...that's common with all vertical smokers.
The door thermometer should be periodically checked for accuracy, especially if you transport the smoker. Mine was off a bit when I fisrt checked it...to be expected. Analog temp gauges are sensitive to shock and vibration, so it is prudent and wise to verify that it is still operating within a reasonable range of accuracy. The SV gauges are adjustable for calibration bu turning the stem with a wrench. If you have a verified digital probe you can place the probe tip close to the stem of the stock thermometer and support it there...close the door and fire it up...when temps are stable get your readings and correct the dial therm if needed...be sure to verify your adjustment until it remains unchanged. The boil-test is the best way, only submerging enough of the thermometer stem under water to get a stable temp reading (don't get the body of the gauge wet, or your probe cable entry point of your digital therm) but you need to know the boiling point of water for your elevation, found
HERE.
Oh, I almost forgot, but here's an old thread from back when I was first tweeking my Vault to get the best performance from it:
http://www.smokingmeatforums.com/t/78485/smoke-vault-24-product-review-mods
A couple years ago I started using washed pea-gravel in the water pan, covered with a double-layer foil liner, then adding water to the foil. The pea-gravel acts as a thermal mass to reduce temp swings somewhat, and it also allows me to run a humid smoke chamber to start, then let the water evaporate and let the pan run dry at some point to create a more developed bark on brisket, pulled pork and ribs, for example. I use this method with all of my vertical smokers now, and it's simple and easy to set up:
http://www.smokingmeatforums.com/a/wet-to-dry-no-foil-smoke-chamber-method-for-smoking-meats
If I missed anything, or any other questions come up, let me know.
Eric