Hi Bones, how long exactly do you plan to leave? When will you leave?
I always recommend the use of pure ammonia for fishless cycling whenever you can. It is cleaner, faster, and easier to control the amount of ammonia you want to add. Typical recommended ammonia concentration during fishless cycling would be anywhere between 2~6ppm.
Since you must take the trip in the middle of the cycling, you can add a raw shrimp or two about a week before you leave home (if) your absence will be longer than just 2~3 days (and if) your cycling is in the stage of nitrite showing up with ammonia decreasing fast. If you only leave for 2~3 days, just increase ammonia concentration to 6ppm you will be fine, and this is especially true when you still haven't had any nitrite reading and the ammonia still stay the same.