I have built plenty to go in the t-tracks (i assume you are taking about for fishing and not for transporting) but I still prefer floor mount since you can get them exactly where you need them. If you have a vertical riser post and fish straight out the front or back 1/2 of your rods will be hanging outside the boat since 1/2 will be on one side of the tbar and 1/2 on the other. If you don't want this, the riser can be built angled back into the boat to help get rods more inside the boat and within reach.
Scott Echols
Hi-Tek Stuff
Crazy Angler Tackle