Tanks don't contribute a lot to elite STFs. They're very DPS oriented so a heavy tank tends to hold a team back more than help.
If you really want to tank at least three ranks in starship threat control is required, and two copies of EPTS and one hazard emitter if in a cruiser. EPTW and attack pattern beta will help get and maintain threat.
If you pick up a copy of tractor beam repulsors you'll be able to maintain the 5KM safe zone for fighting some bosses while slapping nanite ships and probes around if required. I'd recommend TBR to any "support" ship about to STF, it's very handy to control the movement of borg ships and puts out about a 1000 DPS on nanite generators while shooting down heavy plasma torpedoes. This power has a "your mileage may vary" component so don't be afraid to ditch it for something you'd like more if you keep blowing up nanite generators you don't mean to or piss off team mates by knocking their targets out of range.
If you fly an escort (probably the better choice) try to get permanent EPTS or two copies of attack pattern omega. The brace for impact Doff works wonders. The goal is to maximize shield resist and your defense stat for survivability while tanking.
The Armitage is probably the best STF escort, it can easily cycle EPTS and AP:O with pets to help control the field. If you want to go crazy with an Armitage, get EPTS3, Aux2Str1 and EPTW1 with 3 damage control Doffs. Tune your power levels so that having both emergency power buffs up will get you about 120 weapon and energy power and equip a MACO shield and deflector with 2 pieces of the borg set. When ever you start getting shot at you'll cap shield and weapon energy while still having decent aux and engine power. This will put your shield resist at the cap with only 5% bleed thru to hull.
Finally check around the forum. The F2P change makes some of the old information on here out of date/just plain wrong but there's probably a dozen "tank" builds tucked away here or follow this link.