Hi there and welcome to the site!
So you have an OKJ offset and you're thinking about upgrading.
You might first decide what you're going to buy and then decide on the seal.
I think a lot of us use the Lavalock seal around the cooker door. I did. I got mine from this site:
We are committed to developing the most innovative products of the highest quality for all your BBQ Smoker Mod needs.
bbqsmokermods.com
I sealed the cooker door, but I didn't bother sealing the firebox door.
The traditional offset is like the one you have already. Firebox on one side, chimney on the other.
Although the design does a great job, some would argue the weakness is the heat is too strong on the firebox side.
You can solve that problem somewhat with a baffle plate which initially forces heat and smoke to start out low in the cook chamber and then allows smoke and heat to rise up through spaced holes in the plate. The idea is it keeps the front cooler than it would be, allowing the temps to be closer left to right. The weakness of that design is that, although the temps are better, there is still the problem of weak smoke and draft at the front of the cook chamber and more smoke and draft towards the back.
Another option is you can also use tuning bars which are multiple flat horizontal bars which you can arrange and space the way you want which gives you more versatility in tuning the temps inside the cooker.
The reverse flow uses a plate to guide the smoke through the bottom of the cook chamber, and then allows it to rise up on the far end. The chimney is located on the firebox side, so the smoke and heat is then drawn in the reverse direction, across the cooking grates, and then escapes through the chimney. This way, both temps and smoke are more evenly distributed through the upper portion of the cook chamber where the food is located.
Good luck!
