I think this might work. I have a structural beam in the middle of the stand above the sump. I like the idea of having all the plumbing over the sump in case of a leak. Are those the brackets BRS sells for the Pentair unit?Here is how I would do it. I know you said you prefer pvc. I would use silicone line from the pump up to the UV. From the UV to the tank would take me longer to figure out. Since it it going on up to the tank, I wouldn't be worried about air in the UV. It' should flush. I guess the mounting of the the UV could be a problem. I have a T-slot stand to bolt to, and have a set of UV brackets.
Mine. I'm not the best at figuring out these things. I'd probably stare at it for a month before I made a final decision, lol.