Fixed defenses are great against blots, but players at even a pretty low level know to insta-kill them by simply pressing a button (air strikes) or simply go around, which on some maps is very easy.
what i meant in the OP was to not to camp and build extensive field defence but to use them very strategically PAK emplacement is good if you hide it and press hold fire till their tanks are very near by and take them out ( you get heat round after 1 shot) then you have a window where they have armor disadvantage You will almost always loose the PAK after that to indirect fire but you will gain a window to breakthrough.
Same way trenches at CP2 and MG crew in CP1 are good very initially to contain the enemy plus trenches cost no MP so its free and if placed strategically it can deny some caps very early but it requires lot of skill to place it strategically else its a lost cause. It will force him to invest on indirect fire but its free for you minus the build time.
I will come up with a good replay soon after i fine tune the combination for now its totally map dependent i fair well in some in some i still need to adapt this strategy.