This is part 2 to my install of leaf springs which should be somewhere on this site. Keep in mind you can do it two ways, remove the boat and work on just the trailer (the safest way) or block the boat which lifts the boat off the trailer and work under it (the unsafe way, albeit more convenient if you don't have a hoist or don't want to do it at the marina).
I went with plan B, again you can google "blocking a boat" to see how to lift it, I don't want to put it here in case it falls on you. I braced that boat all over the place including extra jacks in case it fell. Since I was doing the leaf springs I figured the brackets might as well get replaced too since gigantic pieces of rust are falling off every time.
If you have an aluminum hull boat you do not want to use pressure treated wood, the chemicals in the wood cause mass electrolysis on your boat hull. I did a lot of research and chose green wood because it's softer and molds to the shape of your boat. I thought about buying that fake plastic deck wood and was glad that I didn't because it's not strong enough and won't support your boat. I bought all my brackets on ebay and got the heavy duty galvanized ones, and bought the u bolts at etrailer.com, they were shipped pretty quickly. I also ordered whatever bolts I could there and bought the remaining at home depot, I went with either galvanized or stainless and antiseized everything. The ubolts that came from etrailer worked perfectly, you have to measure out your beams first though. I used a grinder with a cut off blade to cut through the old u bolts, it zipped them right off. I didn't wear any gauntlet gloves so now I have these really cool burn marks where I held my left arm up to shield my head (I was wearing a face shield, I'm not THAT dumb). You want to wear gloves or a jacket to protect yourself when grinding.
I also went with zinc roofing nails instead of stainless staples. Either will work but I wanted to put a shitload of nails in it and get it done quickly. I went with regular outdoor carpet, when I read online about carpet bunks most people said it doesn't make a lot of difference. The proceedure is simple. Cut off your old bunks, measure them and cut new wood to size. Cut the carpet to size and nail/staple it on, there are a lot of videos showing you how. Since my boat was blocked, I didn't have to do a ton of measurements. I just lined up the new bunks with the bottom of the boat and installed them.
You can see how bad of shape the old bunks were, the carpet was falling off and the wood deteriorated.
These are the new supports that I got from ebay, I measured my old ones before ordering them.
Tools. Note how the old ubolts were cut right in the middle. If you do it this way then they pretty much fall off. You can try to unscrew the bolts on the old ones but I bet you would rather cut them.
And finally the new bunks installed. I try to make it a point to wash down the new supports everytime gigas goes out.