The best mass builders for triceps are:
Close Grip Bench (a grip slightly narrower than shoulder width)
Dips to parrellel (if you go deeper it will activate the chest)
Pushdowns
Overhead DB Extensions (two hands, one dumbell)
In my book these are the best mass builders for triceps. You will notice there are no skull crushers listed. I don't list them because I have seen too many people get elbow problems from them including myself, but you maybe a person who can do this exercise without any trouble. I would train tris once a week with 2 to 3 exercises not goin over 8 sets total. This is what I've been doing lately that has been working my tris hard. I do this after my shoulder workout so my tris are pretty much warmed up. Here it is:
V-bar pushdowns 1*warm up 2sets of 6-8reps (very hard set, i have to start with the pushdowns first b/c of my screwed up elbows)
Overhead DB Extension 2sets of 4-8reps (again just going very hard and heavy, no time for pussy energy wasting sets, when my tris are already warm and sore)
Dips 1set of max reps (this set is usually a long ass set, i keep pumping out rep after rep, and sort of do a rest-pause where i take 5-10second breaks and keep going, this set is only listed like one but feels more like 3)
That's it!! This routine is someting that took my a long time to perfect. I had to work around my elbow problems and find the right balance of exercises that would give my triceps a good workout while eliminating elbow stress)