Inline heater for 10 gallon?

[beepboop]

I have a 10 gallon cold water tank that I want to convert into a tropical tank. I have an eheim 2211 canister filter. I've searched high and low but can't find an inline heater that supports it's 3/8 inch tubing (roughly 9 to 10 mm). I don't want to use a bunch of hose adapters because in the past doing that has let air get into the lines. I also can't find any inline heaters under 200 watts. Is there an inline heater under 100 watts that uses 3/8 inch tubing or has specific adapters made for it? Thanks