Without knowing exactly what you have, and how much distance you need, it will be difficult to make a recommendation.
Going by the fact that you have a powered jack on your trailer, you must have a weight distributing hitch. Extended shanks are available for weight distributing hitches.
The hitch extensions used by most truck campers are overkill as far as distance. You only need a couple of inches, where most truck camper extensions add 18"-48" to the length.
Most of the hitch extensions sold by etrailer.com are limited to 3500lbs of trailer capacity so they will not work for your application.