I know to install the center baffle first but my question is how do you get the silicone down the inside of the outer 2 baffles? they are 1" apart and my fat meat hooks can't reach all the way to the bottom of the tank to seal both sides.
Any help appreciated

Just run a bead of silicone where you want the baffle and slide the baffle into place. THen use a popsicle stick to reach in between the baffles to smooth it out. It won't be the prettiest sump, but it should hold.

You can also use a bead of hot glue to set each baffle. Just make sure you cover the hot glue totally with silicone. Good luck!

First I cut two small pieces of plexi that are 1"x2.2" and silicon them as braces for the middle divider so it can rest on them. Then I silicon in the two outer dividers while I can get my hands between the baffles. Finally I run a bead of silicon where the center divider willbe. I then put in the center divider which rests on the 1"x2.2" braces. That way it will never slide down and gives it something to rest on while the silicon cures. I use the eraser end of the pencil to smooth it out.

I also wear nitrile or latex gloves... it will save you a TON of cleanup and mess.

put the baffles far enough apart so you can get your hands between them, its a good idea to be able to clean your sump if you have too. if you dont want to do that, just silicone one side of it, it will hold fine, look at your fish tank, is there silicone on both sides of the seams? or just one? plus, sump baffles dont realy have any pressure on them

You can clean them with a toothbrush tied to a stick if they are 1". I wouldn't waste valuable space (unless you already have a huge sump) on baffle space.