First thing, pitch the inner tube strips and split a rubber/plastic hose to fit over the rail. If the diameter is too big you can trim it down so it doesn't overlap. If you want to lock them down, a larger aquarium type rubber hose is the ticket.

However, I've been using this same plastic/vinyl (not rubber) tubing I got at Farm & Fleet for about 10 years or so, without ever having changed it.  I started out using the strips that come with it like everyone else for a few years, then went to the rubber lock down tube, then this plastic/vinyl that enables changing the rod angle (with a deliberate effort using the rod in the holder for leverage). If the DE moves from the lures vibration, a quick turn on the easy to get at screw takes care of it. I do have to make some seasonal adjustments when things shrink or expand...but for the most part they don't move much, and the versatility is well worth it to me.

With a low to the water Ranger 600 series type boat you don't have to fight the down rod in and out of the water with this set-up (if you typically like to submerge the rod), just set it in the holder out of the water and pivot the rod down into the water (or back up) to whatever angle desired. Also, being able to adjust on the fly like this allows you to pivot the reel level to crank in baits/boards while still in the holder about 80-90% of the time. I've logged well over 1000 hours trolling with this method, and once you get used to it, I guarantee you'll be looking to bring in boards this way whenever possible (Especially the new giant Church boards). This method has proven to be (almost) fool prove.  

Different subject but along the same lines, I see most guys run the bait out, engage the reel, then put it in the holder under pressure when it's much more efficient to drop the bait in the water and put the rod in the holder while the lure is still on it's way out. When coupled with the pivot deal, setting lines is a breeze, just need some light thumb pressure while paying out line, then let the clicker takeover once the reel is in the holder.

You can also get a different rod going while one is paying out... it's all about optimal efficiency while trolling, same as casting.