first make sure the ohm ratings match your gauges.  i put tube senders in my tanks, which are a benefit in a marine environment since they use pressure to measure tank level and they're not affected by fuel slosh. 

then theres a floater style with the arm thats connected to a resistance style pickup.  since it measures where the float is on the top of the fuel, when the tanks slosh so will your reading. 

the tubes cost more, but they're also easy to install.  measure tank, trim 1/8" away from the bottom on the tube.  install, done. 

tube:



float: