Replacing your old outboard portable fuel tank isn't as easy as it used to be. With the new EPA regulations for low permeation manufactures have taken drastically different approaches that are not always compatible.
Moeller Marine is a leading manufacture marine fuel tanks who purchased the Tempo brand several years back utilizes a self venting fuel cap. The cap is designed to release pressure when pressure exceeds 5.5 psi. This design may not be the cheapest to start with but you don't have the added expense of replacing your fuel line. That's right your existing fuel line will work with no problems.
Attwood Marine has taken a different approach with their outboard gas tank. Their cap doesn't vent so they incorporated a fuel demand valve on the fuel line. This demand valve is designed to regulate the increased pressure from a non venting tank and therefore prevent flooding of the engine. This system is currently being used by many popular boat builders at this time. For worry free performance it is highly recommended if purchasing a new Attwood outboard gas tank also purchase the Attwood fuel line with the demand valve.
Sea Sense Marine best known for their Securestack 6 gallon stack-able fuel tank that is very popular with pontoon boats. These tanks have a built in 5% vapor volume expansion chamber low permeation tank and cap plus a new and improved fuel valve at the tank.