Joe,
why would you want a rod across the transom when trolling, personally I'd highly advise against it and here is why.
I'm not sure if your triolling inshore for stripers or offshore for tuna, but either way that rod is now in the way and needw to be removed to fight any fish off the transom, doing the over under routine with that rod is a pain and will just lead to tangles and lost fish. Especially for offshore fishing, you want a 100% clear transom, especially on a boat our size, even look at expensive battlewagons in tounrnaments, no rods EVER across the transom. They use a rocket launcher to get more rods out but NEVER rods across the transom where they get in the way or fighting a fish.
I would do what oncslr recommends, add a center rigger, I did the same thing and it works much better. I run an 8 rod spread when trolling offshore.
I run 2 rods off my center rigger, it is double rigged. I run one WWWB off the top clip, that rod goes in the top hardtop leg, my shorter down the middle goes on the opposite top hardtop rod holder. My outside rigger rods go in the lower hardtop rod holders on each side. My inside rigger lines go to the fwd rod holders in the cockpit and my flatline rods are at the rod holders at the back of the cockpit. This gives me a free transom to work incase we hook multiple fish, and if rods go off, none are crossing one another and they can release freely and and easily be worked to the center of the boat to fight the fish. If we had rods down the middle off the transom we'd have more to clear before we could even remove a rod from the holder and begin to fight it, not to mention you will never get that middle rod out far enough and have it run right with the line dipping in the water, a center rigger really is the way to go.
It might be nice to place rods at the transom for the rides in and out of for inshore fishing, but other then that they really are more a hinderence then benefit, I'd strongly advice not using them for any trolling. I've mated on lots of boats in high school and only 1 had rods acorss the transom, we had 8 rods go off at the canyon and 20 min later we had 3 fish in the boat, all the rest tangled and or came loose because we had to clear lines at the transom or had to do the over under routine way too many times. I had to respool 3 rods on the water just to get them back in, what a PITA...here we are in a hot tuna bite and I'm respooliong 50W reels because we just had a huge tangle with 3 rods because the transom rods were in our way. After that trip we never again put rods across the transom on that boat.
As a side note, I removed all of my hardtop rod holders and removed my third set, I brought down my 50W's and placed just 2 sets on my hardtop legs and spaced them and angled them so that when a fish is on the tips will never hit or touch and that both rods and reels are safely within reach from the cockpit so getting them is not a problem. I called Lee and had to have new bolts and backing plates sent, my old ones were junked, cost was maybe $15 a holder, but well worth it to have rods where you want on your boat.