I am the skinny guy who builds wheels for folks who are often twice my size and for our custom tandems which have to handle even more abuse.

Am thinking that the stock 32 spoke rear on the FX is not going to be up to the task as it stands and may provide better service if it is hand tuned and if the rider is not one that is hard on equipment... add some curb drops and rougher terrain and that stock wheel may not remain straight and true.

The Trek FX is a pretty solid bike and I do not have many worries about it holding up... the wheels would be fine under my 145 pounds but were not designed or built for someone who is twice that size and then some.