Traditional layout mounts like the Lee and Lee, Jr. are very strong and work great. Downside is getting past them on the walkaround and having to lay them down aft if there are low bridges to pass under.
The Taco Grand Slams also work very well. The heavy-duty units should be used, and our 15-foot HD riggers have thousands of miles of running and hundreds of hours of trolling use. No issues at all.
Brian