Where is the install and do you have access to the inside attic areas beneath the panel mounts & what is the roof composition? Spreading out the area is a good thing, as well as using roof slope and gravity to stop water wicking identical to shingle design. That is a neat system and I know one home owner who wishes they'd had it, though it would have required twenty-eight(!) of them in addition to the QD brackets.
I just removed this system from a local house, the roof was asphalt shingles and over twelve years the weight and HEAT on the 3"x5" foot-print of the panels' flush mounting brackets had welded shingle layers down to deform the roof line and created valleys around them that worked to collect water. In hotter climates I see the extra rail system might help keep through-roof mount systems cooler so they'd weather better.
I'd sure go with a slow-cure solvent-based polyurethane sealant instead of silicone, Trempro 636 is very slow, meaning highest ratio of solids to solvent so very little shrink and has very little silica texture in it to better seal metal to any surface. I've seen metal layers interior sealant of that still pliant after 40 years. Good stuff.
The far left set of panels had been installed with Silicone and although the sealant was still there and not shrank or degraded in itself, it HAD lost its bond to both the metal and the shingles, simply held in place by 1/100th its original bond. Those brackets came away with only the top shingles surface granules attached to the caulk. The other panels were all done with a butyl rubber sealant that suffered some cracking and could have used refreshing every five years but otherwise showed nearly perfect sealing - and had to be cut out with both layers of shingles from beneath them.
