Hitch extention just adds to the cantilevered leverage the tounge weight has on the rear of your tow vehicle. Will also make steering input more sensitive when backing up. More of an issue the shorter the trailer.
Safety chains can be adjusted as needed to suit the load/tounge sag by putting a few twists in each chain to tighten up slack. My 20' deckover has chains that always need a few twist to not drag, even unloaded. Another trick is to cross them, right chain hooked to left on bumper, left chain to right hook point, makes an x under tounge. Does two things. One, you can tighten up each chain with more twist and less sag because they will get more sag when you turn, and two, if the hitch comes off the ball the crossed chains make a sling to catch the tounge instead of it falling through the straight chains to the ground due to loser chains, catching and snagging and over powering the chains and just ripping them off, and becoming totally detached.
Trailer towing is an art of its own. Good luck... nice trailer by the way...