I have fiberglassed a number of ABS printed parts for strength and improved final finishing when used in a display model. Typically, these were thin wing and tail sections.
Epoxy resin is not optimal for adhesion to ABS plastic, even if the ABS has been sanded and given some tooth.
What worked best for the thin ABS parts I was working with was to "glass" the parts with 1 or 2 oz glass cloth and thin CA glue. This bonds permanently with well sanded ABS and the glass cloth. Added measurable strength.
An additional advantage is that the layer of glass prevents solvents from getting to the ABS and bringing build layer marks and joints and such back into view, "printing" back to the finished surface over time.
This technique is not designed to add lots of composite strength for a high power rocket, but could work well if thoughtfully used on low and mid power models.
Another useful way of adding strength to thin ABS parts is to grow a channel in a thin part for a carbon fiber shape. After the grow, CA the carbon fiber spar into the part. Instant structural strength.