Oh wow!!! I thought it was the grey nylon handle in the photo, but after another closer look it is wood. You have an older model as they went to the grey nylon starting in the 2000 year model. What's the date code stamped in the top vent? Also if you replace the top vent, make sure you keep that date code as Weber will ask you for it and that is how they determine what series of parts to send if you order more (plus warranty info, if any still applies). It should be either a single or double letter code stamped in the silver metal of the vent (may be faint).
I'm not sure exactly what is involved in riveting in the replacement vents but I'm sure it can be done. As to the water pan, it fits in the bottom of the smoking chamber below the bottom rack but above the charcoal ring. Should be some little stepped tabs on the inside of the mid section, water pan goes on the bottom step and bottom food grate goes on the one above it. Traditionally you fill it with water to help moderate the temp swings and some would argue to add moisture to the smoke. Remember it takes a good bit of energy to flash water to steam so it helps to keep the temps from spiking like it would without the water or some other mass to "moderate" the swings. You can cook without a water pan, and if you are doing a higher temp cook at say 375* for chicken, you would leave it out anyway. That's the beauty of a
WSM they are very versatile and can be configured different ways.
Did you get all the parts? Should have the following:
Base (clearly visible in the photo so you have it)
Mid section (same here)
Dome top (ditto)
Mid section door
Top cooking grate (goes in mid-section)
Bottom cooking grate (goes in mid-section)
Charcoal grate (smaller than the two listed above and goes in the base)
Charcoal or fire ring (round thing with holes in it that sits on the charcoal grate)
Water pan
I think that's all the main components. If you are missing any parts, post here before ordering from Weber, as there are usually local alternative sources for most of the parts except for the body parts. Grates, water pans, etc... can usually be found locally or a local substitute such as making a fire ring out of expanded metal sheet will work just fine (a home depot stock item).
I added a 2nd charcoal grate turned 90* to my original one and wired the two grates and the fire ring in place to the two charcoal grates. Turning the two at 90* gives you a smaller space between the grates and you have less trouble with small pieces of charcoal that might still be good and lit falling through the grate. I also added a BBQ Guru DigiQ2 power draft, but there is no need to spend that sort of money up front and it's probably better you learn the smoker without a digital controlled power draft (it makes the
WSM into the Cadillac model and as close to set and forget as you can be with a charcoal smoker).
Man I could ramble on for days about a
WSM and there are a lot of us here that swear by them. The
WSM is a sweat smoker and is somewhat forgiving due to the design. Again, I strongly recommend spending several hours browsing the TVWBB website as it's mainly dedicated to the WSM smoker and other stuff is secondary there. Lots of photos, videos, etc... info on basic intro smokes for the first time and it just goes on from there. The owner of that site is tied in with
Amazon and well known at Weber. The Weber customer service folks will also suggest you visit the TVWBB site.
Start at this page as it has cut-a-way photos. Just start reading, follow the links, look at the assembly instructions section (to make sure you have all the parts, what they look like, and how they fit together, etc....)
http://www.virtualweberbullet.com/tour.html
And when you are ready, go to this page and start smoking. You can go with a beginner smoke, or if you are feeling froggy, just jump right in where you feel comfortable. Once you have graduated to the 18-20 hour pork shoulder overnight smoke, you are ready for just about anything.
http://www.virtualweberbullet.com/cook.html
You are going to love the WSM though........ And like I said there are plenty of us in here that love them too and can give advice specific to the WSM. Just remember - post often, and include photos!!!!