Has anyone attempt to mount a Lowrance HDS with the StructureScan 3D transducer in a kayak? I am curious on what it takes to mount that monster, and what sort of battery is required to power those two computers.

I have that exact set up on my ATAK 140. It's an HDS 7 Gen3 with the SS3D. I use my flex pod to house two batteries wired in parallel to power the Lowrance, and two batteries to power the SS3D. I bought a ram transducer arm designed for the original SS and had to drill out some holes to mount the SS3D but you can make it work. It's really not as daunting of a task as you'd think. To be honest, you could get away with powering the whole set up using two SLA batteries in parallel if you had to.

A couple of thoughts after I've had this setup for a while:
1) SS3D is a cool concept but you need to be paddling a faster speed to get really good mapping. Is that feature alone worth all the money? I'm leaning towards no...BUT
2) The side scan/downscan detail is awesome! I use the side scan 99% over the 3d. You get better coverage in shallow water with the SS3D, and with the level of detail you get this makes it worth it in my opinion.

Thanks for the ideas. The SS3D is so new and expensive that it is not too common to see in kayaks right now. It is crazy expensive though and would most likely be the last electronic I would ever buy for the rest of my lifetime, maybe. I want to use it on a kayak with a pedal drive system so a 3-5 mph trolling speed is easy to achieve for the SS3D to cleanly map the terrain.

This magnetic transducer mount is an excellent choice as an alternative to drilling: http://www.fishfindermounts.com/product-page/xpower-15mm-magnetic-transducer-mount.

I have measured the HDS7 Gen3, HSS2, and all the cables. I think they all may fit inside a Group 24-31 Battery Box, with an AGM EXT16 battery. This is a portable setup I am contemplating. I don't know if the ext16 battery is enough to power all the devices for a full day of fishing though.