delivers1234, Your use of the dish antenna mount as a base should be fine given the antenna you have. They are pretty strong and you've got the outriggers to boot. You don't have near the amount of wind load that a dish would create although the longer the taller the mast you have above the dish mount, the more leverage is created against the mount. From your photo however, it's hard to tell how tall your mast is for the antenna. Band clamps are pretty strong but as ramal121 pointed out, you have two round objects mated against one another and there is the tendency to twist against each other. (Think of closing a pocket knife) This could still happen with two piece of square tubing mounted side by side so I wouldn't lose too much sleep over this.
I live up in the Bay Area and like you, we don't have to deal with lightning storms as much as other parts of the U.S. We're not immune however. It would be a good idea to eliminate the insulating hose/piece you have and create a decent path to earth if you intend to keep that up for any length of time.
For peace of mind, I'd suggest keeping your clamps and adding long, stainless steel bolts through the top and bottom of the two tubes along their mating surface. Then, work on the ground issue. As far as the last photo you posted of the no-hub sewer clamp, don't use that at all. It won't be of any benefit to you.