Trailers take most of the strain so your wheels should be OK.
I would worry more about your transmission. Switch your cassette to a larger one, at least 28t, bigger if your rear mech can handle more teeth.
Consider using an MTB style of chainset to get lower ratios. You can put your original one back on for regular riding.
You should also consider switching your low end bottom bracket for a better one such as Shimano UN72.
Fit some alt. handholds such as bar ends or a small clip on aerobar.