I have a 2004 Itasca Meridian with the CAT 3126E engine. This engine has one fuel filter.
Here are the filters I use:
CAT Oil Filter 1R-1807 (preferred)
NAPA Oil Filter Gold 7791
CAT Fuel Filter 198-6378
(Alliance 32FRT03) (preferred)
32FRT01 is a 30 micron filter
32FRT03 is a 02 micron filter
Racor P/N S3203 is 2 a micron
Wix 33788 is a 2 micron filter
IF your engine has only one fuel filter, you should use the 02 micron filter.
Be advised there seems to be controversy concerning pre-filling filters or installing dry. He has a good video at: