Master Sapper and frenzy charge generation

I decided to play a build using the Raider ascendency because of the frenzy bonuses. I think I see now why so few use this ascendency. I have 8 max frenzy charges and when they're up, it's fun. I haven't started in maps yet but I think the monster density will make it pretty easy to keep the frenzy charges up. My issue is against bosses. I just did merciless Daresso last night and there aren't things to kill to gain or refresh frenzy charges. I'm bot sure about all the map bosses, but I'm sure at least some of them will not have minions to kill as well. I'm using spectral throw so i'd have to melee hit if I wanted to use the frenzy gem. Not ideal since I made a build that's designed for range and projectile damage. So I've been looking at options and this leads me to my question:

Master Sapper gives a chance to generate a frenzy charge when enemies trigger a trap. If I link to cluster trap and/or multiple traps, does each trap give an independent chance or is it one chance per throw of traps? I know that charges on skills are usually limited to one charge per skill use. So I was wondering how multiple traps thrown by a single use of a skill was the same way.

My other thoughts for generating charges against single targets are Doedre's Elixer (have to fill up my belt with these if I want to get to 8 charges) and Victario's Charity shield (5% chance to give allies a frenzy charge on hit) and Necromantic Aegis to give that mod to minions. I guess that would work but I'd lose a shield slot and some passive points getting that node. Most of the passive frenzy generation options require kills to proc. Maybe if they gave the Raider something more unique like chance for frenzy charge on hit instead of kill, more people might choose that ascendency.

It's per trigger, so in theory you can get multiple charges from one use. In practice the chance is so low, that sometimes I don't see more than one charge for a whole map on my trapper (no investment in charges though).

It also won't work too well on a non-trapper build, since base throw speed is 0.5 sec and you will need multiple throws to get your max charges, then trap's limits of 3 uses and AoE killing the traps before they arm come into the picture, and it becomes even worse.

I would probably look into something with Writhing Jar and Frenzy to generate charges in boss fights.

Bow Raiders are quite good, in my opinion, always fast, phasing, ele status immunity, dodge, always max charges for pretty much free (frenzy is so fast, you can max out in a couple of seconds even on single target). It's a fun ascendancy, doesn't need to be the best, I think. Sure is tricky for Spectral Throw, though :).