Building fuel tanks is a delicate matter, especially for boats, where safety must be your very first concern. Usually boat fuel tanks are built out of stainless steel and/or diferent plastic materials. You can find all sorts of fuel tanks on the market, from special fuel resistant PVC to a fiberglass and epoxy build fuel tanks and steel tanks. For a small boat, the best and cheapest thing to go with is a simple plastic fuel tank. They come in variety of sizes and shapes so you can find one that fits your boat best.
I usually preform some modifications on my boat before summer and this year I decided that I will try to gain some extra space under the back seat of my boat, and decided to modify the double bottom of my boat and install a custom made boat fuel tank inside the double floor. Of course my boat wasn’t designed for this kind of fuel tank so I will naturally have to modify everything. By this I mean, that I will need a little extra strength to be added to the original bottom and make some kind of fuel tank brackets that will hold the tank in place. I will also need a custom made fuel tank.
So I decided to try and make one my self. At first I tought I could make it on my own, but soon I found out that I am not an expert welder and that I will have a lot of trouble getting it all together, so I decided that I will make all the parts and than have them weld to an expert welder. I cut open my double bottom and started taking some measurements for my fuel tank and brackets. I than designed a full 3D model of the fuel tank using my famous 3D modeling software. I also made a dummy fuel tank made out of cardboard papper, just to have the abbillity to check if everything fits well before I actually build my fuel tank.
While I was in search of a knowledge on how to build fuel tanks, I found two very usefull articles about this topic. The first one is Building A Custom Gas Tank, where you can find a lot of pictures of the building process and a simple boat fuel tank plan. The second article talks about building a fiberglass fuel tank from very light weight foam and fiberglass and vinyl ester resin. You can the article here - Composite Fuel Tank Construction. I suggest reading it becouse it has a lot of usefull information about building a composite (fiberglass) fuel tank.