Hi Martin, welcome to the crew.
Although generally a pit will not get hot enough for the galvanised metal to be much of an issue, it is generally not considered a good thing to have it in a cooking environment. Now, not sure if it has closed yet or not, but the site was offering free plans for a smaller type smoker, you just had to stump up for postage etc. Have a look at it.
And a tip. if you go for it get the extra files to enable you to hand over the files to your fabricator (who hopefully has a cnc plasma/laser/waterjet to cut out all the parts. Just a thought.