Steven,

Doesn't leaving the tanks partially empty cause problems with condensation
or something along those lines?


NO! That is another of the many OWTs in aviation (old wive's tales). Cessna
did extensive experiments in a clima chamber. They could NOT produce any
noticable amount of water in a fuel tank no matter what they did to the
temperature. There are only two ways to get water in your tanks:

1. it's coming in with the fuel from the truck or depot tank.

2. it's been raining and your fuel caps leak.

In any case, there are very, very few GA single engine planes where you
don't have to constantly work with the fuel vs. payload trade-off. Always
filling the tanks robs you of a lot of the potential the average GA plane
has. Or your cheat and fly overweight - which is not the smart alternative.


--
Thomas Borchert (EDDH)