According to SOWPODS (the combination of Scrabble dictionaries used around the world) there are 6 words with the pattern -U---U-ER. That is, nine letter words with 2nd letter U and 6th letter U and 8th letter E and 9th letter R. In alphabetical order, they are:
curiouser
multiuser
outhauler
outpourer
puncturer
succourer