the rod holders that i use for tuna trolling are a combination of two.
i took a smith outrigger rod holder http://www.tackledirect.com/ce-smith-outrigger-rod-holders.html
and bolted on the largest clamp on rod holder to make a single piece. http://www.tackledirect.com/ce-smith-53661a-2-way-clamp-on-mid-mount-rod-holder-silver.html
the outrigger tube is just a little too wide for the clamp on rod holder to fit around. what i had to do was squeeze the outrigger tube in a big vise and get some longer 18-8 stainless steel bolts from west marine. make sure you grease the bolts and you should be fine.
when i'm trolling for albacore, i have the 5.5 foot rods pointed straight back vertically and the 6.5 foot rods pointed straight out horizontally. that gives me a pretty good spread without the hassle of outriggers. very simple and clean. i like to run the clones, jets, cedar plugs or rapalas back about 75 feet where the prop wash ends. with everything even, i can do some pretty tight turns and not worry about tangles