I have a 99 310 Sundancer I have...

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I have a 99 310 Sundancer I have replaced both fuel gages still do not get accurate readings 

How hard is it to locate/replace sending units?

[wingless]

Likely very difficult.

On my 2000 380DA is is possible to see the sending units, w/ the cockpit deck, behind the cockpit side walls, located inches above the unit.

On my boat, it is therefore theoretically possible to locate the spot in the hidden deck compartment to drill an access hole, then swap out the sending unit.

It may be that a replacement provides identical results because of the tank shape, attitude in the boat and resistance versus float movement.

A much better option is to install fuel flow transducers and instrument that monitors in/out flow from the tanks for exact display.

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That was my initial thought but haveing hard time finding a fuel flow instrument do you know a brand / manufacturer for them

[wingless]

There are many options.

Here is FloScan.

http://www.floscan.com/html/blue/recreationalmarine.php

[gtstang462002]

Look at untrasonic sending units or straight shaft units. They provide more accurate readings than the long bent arm units.

[Pigpen]

A bunch of us on the 390MY FB forum have successfully used this one. The tank is 24”deep and used a 23” unit. They come in various lengths. The accuracy is spot on. As far as access, look directly above your sending unit and there should be some kind of access, I had to pull up some carpet