36" would work good for 3 rods per side. but I have extra holders that I use for net holders. I have 2 nets the one I use and a spare I use if the first one gets tangled. if you plan on using net holders or extra rod holder to store your net I suggest getting the 48" tracks. its really nice having the net already ready to use. think about it a little before you buy.

another thing to think about is downriggers. if you plan to put riggers on later and mount then on your trachs then you'll be glad you got 48" tracks. and if you can use machine screws with backing and nuts to mount the track. if you don't have much room for a backing you can just get fender washers. its always better to have extra long tracks than it is to come up short. before you buy check out amazon for holders and tracks.