flexible fuel tanks for diesel

I am looking for information about permanent below deck installation of flexible diesel tanks. I am building a 32' sailboat designed by Mark Smaalders. I want to install the diesel tanks under the cock pit sole, and make them accessible from the engine room. Two 37 gallon Nauta flexible tanks would fit nicely on enclosed shelves port and starboard. I can't find good information on how to install the tanks, and whether they can be used as the primary diesel supply. For instance, how would I route the return lines? Are the tank fills flexible enough to tolerate the rise and fall in tank volume and not pull lose? How do you monitor tank volume?
Appreciate any help or advice you can offer.

 

http://www.atlinc.com/US/marine.html Another manufacturer.
Installation must be inside a compartment. Installing a "day tank" simplifies hose routing when return lines aren't needed for the bladders. Monitoring with a flow meter or simply counting how many daytanks have been filled. If you intend to do some ocean cruising there should be also another bladder for ballast water to be filled with the same volume as the fuel has been consumed, or alternatively, an adjustable wall. Either one is used, it's meant to hold the fuel bladder firmly in place...
Teddy

 

Bentwood;
Glad to see you made it. I hope you get the info you need.

 

You have yourself hight lighted the problems with flexible tanks.

As far as replacing fuel used with water ballast ??????????

But shifting tanks, leakages, contents all a no no