In need of some advice

I've been smoking great brisket with a COS and burnt the firebox up this past season.  I'm starting my first reverse flow smoker on a trailer.  The smoking chamber is a 30 inch diameter pipe with a 5/16 wall thickness and its 7 feet long, it weighs in a 694 pounds by itself.  My first question is what size axles do you think I need?  I wanted to go with a complete axle assembly from northern tool.  It has a max load weight of 2,000 pounds, it is pefect width 60 inches.  Do you think that is sufficient or do I need to go with a 3,500 pound axle?  The problem I foresee with the bigger axles is that are all around 74 inches wide which will create havoc trying to access the smoker because my plan was to have it centered on the trailer.  I was intending to be able to operate and open the smoker without having to climb on the trailer.  I wanted to work it all from the trailer side.

Next I was planning of building my main trailer frame out of 3inch channel iron to keep it beefy.  What do you most commonly see these types of trailers are made of?  If you see a flaw in my plan please let me know.

Thanks