Does anybody know if Bigelow inflatable technology could be used for
making fuel/oxydizer tanks? The main weight problem for a Mars mission
is the fuel/oxydizer. With inflatable technology it would be possible
to launch all the combustible *and tanks* using a small vehicle. The
capital costs for designing, building and operate a small reusable LV
probably are within the possibilities of private companies. NASA could
buy fueled tanks in orbit for using for their missions at far less
price than using Ares V.

It's been looked into.
Stress upon takeoff put upon the membrane makes this notion unmanagable.

Are you talking about the same mission?

The suggestion was to launch the tanks empty on a small vehicle,
inflate the tanks, launch the fuel with several separate flights of
the same small vehicle, and fill the tanks on-orbit.

Of the top of my head, I don't see why the takeoff stress would be any
worse than for launch of a Bigelow/TransHab-style habitat.