I spent most of my early life on the bench as a tool maker, and have very strong hands and mad skills at that kind of stuff, I just bent those V braces near the bow by hand and screwed them down to the frame. I wish I had a welder ( I used to TIG weld molds as part of my job, and had all the correct certifications to weld aircraft and stuff, but that was a long time ago), I don't have a welder anymore (but wish I did). You will find that 1/4 x 1 inch aluminum is very easy to bend and form by hand with just a simple bench vise, I just eyeball everything as I go.
I got all the aluminum at either Home Depot or Lowes (Lowes usually has a better selection). If you live near a big city with manufacturing, you will find aluminum much cheaper at metal supply companies, (unfortunately where I live in Sarasota FL, there is almost no manufacturing to speak of, I come from up north where there was a supply place on every corner (Chicago area).
Keep in mind on my setup, the boat hull itself is part of the structural strength of the trailer. Those 1 inch sq by 10 ft aluminum bars (1/8 wall thickness) have 3/4 sq steel tubing inserted inside for additional strength. I then sealed each end of the 1 inch tubes so water can't get in to rust the steel.
The original design didn't have that V brace re-enforcement supporting the 1 inch sq tubes just ahead of the rear cleavis pins, but after a couple uses, I could see those cleavis pin joints were taking a lot of stress so I had to devise something to help re-enforce them.
The nice thing about the Harbor freight trailer is it's really cheap, but has all the certifications and certification plaques to be able to go to the DMV and register as a utility trailer, so you can avoid the inspection and certification needed on a home built from scratch trailer, as a professional engineer (what I do for a living) a guy like me would be the one who would be needed to certify stuff like this, (this is not my area though so I don't have the transportation certifications that would be necessary, (my area is industrial), that's why I just bought the Harbor Freight trailer, and modified it to do what I needed (it's cheating but a lot cheaper than going to a certified trailer maker). Actually that may not be true, I have a friend in that business (making trailers) who looked at it after I built it and he said he could have done one for me for not much more than what I paid by the time I was done (probably more as a favor though), I think mine ended up costing around $300 by the time I was done. It's been working now for about a year without too many issues, but the steel parts are already starting to rust ( a Florida salt water thing), I will need to replace the steel with aluminum probably in the next year or two.
Actually HF sells small boat trailers (basically all ready to go just add the racks for just a little more, mine was unusual because my boat is 20 ft long (with the bow sprit) so I had to go custom, and mine also doubles as a kayak cart, which I thought I would use all the time, but in reality I don't (a lot of extra work for nothing LOL). As long as you don't back the trailer into the water at all, and make sure you rinse everything off really well after going near any salt water, it should last for a few years anyway. The way I figure it I will just replace the steel stuff as needed with aluminum as it rots away. The rusting problem is mostly a Florida thing living near the salt water and the high humidity all year round ( I only go in salt water (Canadians are scared of gators ( LOL)), if you lived and used further north in mostly fresh water it would probably last for years.
Here is the Harbor freight page showing the trailers ( http://www.harborfreight.com/catalogsea ... q=trailers
). Since you are mounting Outbacks (vs TI) instead of the absolute cheapest (like I bought), you might look at a little better model almost ready to go for around $300 bucks.
I found their trailers (that come in a box) pretty east to assemble and build, I clear coated everything once finished in the hope it would make it last a little longer, and replaced some of the structural screws with stainless nuts and screws.
I just store the whole works (boat on the trailer) in my garage so I'm ready to go out any time, it works well for me. (this means you would need good support for the hulls so they don't collapse during storage). I found that sliding the kayak on PVC tubing mounted lengthways on 11 inch centers seems to be the best way to store the boat on the trailer (like Kayakman7's setup), I think he used 1.5" PVC, I just copied his idea . We both have TI's, but I think the Outback has a similar bottom (two long keel grooves the length of the boat on 11 inch centers). Possibly some with an Outback can jump in here.
Hope this helps