I have made some of these. I am sort lazy, so I don't want to type it all out, but if you call me I'll tell you all about how to make one. Seriously. You'll probably have to leave a message, but I'll eventually call you back.
Peace and grease
if you want to make your own the best way is to find a used cheap gas tank you like the shape of and cut off the back hump shape, make a flat pan out of at least 16ga metal to attach it to then use L shaped metal to make attachment points to your frame or attach to old hinge brackets its up to you. A picture says a thousand words .So look at this link it has a few pictures so a few thousand words on seat building.I used to original tanks that came with the cbs and then I used a honda cx delux gas tank for the tank.So you end up with a nice big bread box tank and a small custom solo seat in steel.My latest project another cb360 I bought a upholsterd glass seat.The glass seat has no mountings of any kind so you have a 200 dollar seat you still have to fabricat mounting brakets as you would a steel seat.so either way making your own from scratch in steel or buying a prefabed glass shell.same amount of work.
Its cheaper to buy a fiberglass seat then to build your own glass seat .if you can weld or pop rivet metal a steel seet is cheaper and easier to fab.
Here is my condensed "10 easy steps to make a custom cafe seat in the comfort of your own garage in just one weekend!" Take it or leave it, it's free advice that worked for me. This is just one way to do it -- not even touching on vacuum forming, or welding anything up. I am sorry that I don't have any pics to go with this -- My hard drive crashed, so only the most basic text is all you get. Hopefully it is enough to get someone started.
1. Safety is important. It is no fun if you build a nice seat, and then die when it is done. LOL! Use a quality filtration mask (respirator) and safety goggles whenever you are sanding any of this stuff. Fiberglass dust will not make your lungs happy, I promise. Working smart is not just for retards.
2. It is really hard to sculpt a nice round, symmetrical shape. It is even harder to make a nice, round shape AND make the apex of the curve right in the middle of your seat. This is good to know up front so you can be thinking about it every second you are cutting the foam.
3. It will look twice as bad once it is all nice and shiny unless the shape is right up front.
4. I think that the easiest way to shape the foam is to use a large abrasive disc fitted to your drill. Most foams are easy to sand to a nice smooth finish, and the disc-on-a-drill thing is a fast way to get the basic shape that I have always found easy to work with.
5. Cutting and sculpting your foam will make a huge mess. I mean the kind of huge mess where the dust will get into everything and in the corners, and under everything, and everywhere, and a year from now you will still be cleaning that stuff up. Wear a dust mask because it will be in your lungs too. If you have a little tent or something where you can make the mess in a contained space, that might be a good idea....
6. Don't be afraid to use some Bondo on the foam before you lay the fiberglass. Have I mentioned yet that it is really important to get the shape right before you do the fiberglass thing? Also it is very important when actually laying the fiberglass to make sure there are no bubbles stuck in there. It can be hard to get them all out, but they will be major problems later if you are lazy about getting them all out.
7. That cheap green planters foam that your Aunt Minerva uses with all her fake flower arrangements makes a fine base to sculpt. Great Stuff (expanding foam in a can) also is a good product for this application. If you accidentally remove too much foam you can easily build it back up with great Stuff -- but remember that the stuff is also a glue, so it is tough and super hard to clean up. There is less in a can than you think, and if you spray a lot out at once, it will expand more than you planned, so apply it in thin layers until you are used to the Stuff.
8. Since you are making it yourself, why not do something different? Please do not invest a million hours into this project only to have yours look just like every other gay solo seat in the universe. If you are going to make it, please invest the effort to do a good job. Geesh.
9. When you think you are almost done and you realize that it is all screwed up, don't fret it. The thing is made of fiberglass. There is no starting over with this stuff. Just sand it back a little and build it up. Repairs and corrections are not half as hard as you think they will be when you first realize that they need to be done.
10. And my #1 most important (or is it #10 most important?) point of free advice is: Don't try to make it perfect. Pretty good is a fine goal, especially if this is your first attempt at something like this. When you are shooting for perfection, every flaw stands out like a spotlight in the dark. Perfection will take three times as long and cost at least twice as much -- and then it probably will not look all that much better. But if your goal is "just" pretty good, then it will help you relax and enjoy the process.
There is an level of art and craftsmanship that can only be accessed if you are enjoying your work. It is a law of the universe -- If you are all pissed while you are building, you will be all pissed when you are done. It is that simple. I recommend that in your pursuit of just pretty good that you let a lot of the little flaws slide. Unless we are talking about major out-of shape issues, almost everything else can be fixed with some glazing putty and a bit of sanding during your final coats of paint. Up to then, just chill and do it. The rest will take care of itself.
A bird in the hand is always greener than the grass under the other guy's bushes.
It's a two-part expanding polyurethane foam. Just mix Part A and Part B, and it expands and hardens. It's easy to shape with a Surform rasp, woodworker's rasp, and sandpaper. I got a sample pack of it from my neighbor Paul, who works for an auto design studio. It's what auto designers use when they need a big foam block to carve.
The main drawback is that this shit is as toxic as the Fumes of Hell Itself. (Just think about it. What kind of nasty-ass chemicals get really HOT when you mix them together, and then foam up to ten times their original volume?) You don't want any of it on your skin or up your nose, that's for sure. So use a 3M Dual-cartridge Organic Vapor Respirator, and chemical-proof gloves when you mix it.
After I carved the foam into shape, I covered it with three layers of fiberglass cloth and resin. After the resin hardened, I just carved out all the foam, so the cowl is a hollow fiberglass shell.
Use the 3M respirator and gloves when you are working with the fiberglass resin, too, or your brains will turn into oatmeal.