ReneeG
It is a 2 hole galvanized bracket for 6" PVC pipe available at any plumbing wholesaler. The bracket is specifically sized to fit 6" PVC pipe. It is made in other pipe sizes as well.
The bracket is attached to the outside frame using self taping screws.
The steel is softer than I thought.....go figure LOL.. Getting the self taping screw to go through the steel was not hard at all!
As I mentioned earlier it was simple enough to put together and attach that I made an 2nd 6" tube up to carry my fishing rods, which were always a transporting nuisance.
6" PVC pipe can be expensive,hopefully the wholesaler will not charge you straight retail prices.
The good thing about the tube is it is very durable. I used the same tube on my prior TT. I just re-sized it to fit my current 5'er.
Lastly security of the tube is not a big issue with me. I store my RV at home. However you could easily drill a hole in the screw on lid and add a padlock if you like.