We built our extended run fuel system from Mercury Outboard fuel hoses and parts, and the "Upper Red Cap", which is specifically made for Hondas (I think an "Upper Blue Cap" is available for Yamahas, too). See similar system at this link:
BERGS Dual Feed Extended Run Tank for Honda WiseSales.com
We purchased "Upper Red Caps" and Mercury fuel hoses and fittings online, mostly through Amazon.com, and an outboard fuel tank at WalMart; then, put all the pieces together to approximate the system in the photo above. I think we saved $30 or $40. However, it took a lot of online research to find the correct parts and the best prices. So, it might be worth it to just buy the finished system, if time is limited and money is no object.
One advantage of our home-built system is that the Mercury hoses (with priming bulbs) are available about anywhere that sells boating supplies, including WalMart and West Marine; so it's easy to find replacement parts if you damage or lose something. Also, the extra fittings allow individual hoses and caps to be added/removed from the system to configure for either one or two generators; and the fittings contain valves so they don't leak if the mating part is removed.
I think Camping World carries the "Upper Red Cap" and some extended run hoses. So, if there is a store nearby, you might be able to get a closer look at the parts needed. That's where we first saw a system like this, but their parts were too expensive.
The "Upper Red Cap" is pricey; but after you get a look at it in hand, you'll see that it's well-made, and the price is fair compared to other extended run fuel caps on the market.