Well the GTT does have much armour to support it againist Heavy attack or any attack at all to be honest @.@ while the GAB depending on which form can take a heavy beating

GAB 25M Tank Form: The only weakness is its treads so try to take them on face first. try to spin from side to side on the spot to stop them attacking you treads use your drills and cannon to rip other VS a new eject point. the drill drive works great on troops

GAB 25M Spider Form: All you weak joints are open try using your side steps as much as you can in a fight a good GAB pilot can take down a PTX if you can master you side jumps and you hover cannon attacks just try not to stop for too long as it makes you an open target. of your at a distance try to aim your attacks then rush them in tank form and switch to finish them off quickly