I've been running vanguards, just thinking about getting into HQs now, and this has been something I've been wondering about as well. I google and found this spreadsheet:
https://docs.google.com/spreadsheets/d/10zZ1e5X5Xeggzq9ltTwqu2YJdxaIgv-T3FM1m5dmFuA/edit#gid=839958039
I used pyfa as a cheap way to look up the fittings to bring it current on my local copy as of now, anyone that wants to replicate will probably have to do the same. We'll assume .5 space where concord hasn't already spawned as a worst case scenario.
Here are 3 scenarios:
If we take a vindicator with a single PithB, an AIF II, a DC II, and the rest LSE or bulks, it looks unprofitable. According to this spreadsheet, it would take 24 T2 catalysts to take this vindi down. Dropable modules of 445M isk or more and this becomes profitable, given n exact 50% of the value is dropped. With only 1 pith B, this becomes a shot in the dark and doesn't seem profitable, but is easily doable.
If we take a vindicator with dual PithA, a DC II, and the rest LSE or bulks, it looks like we have a shot.. According to this spreadsheet, it would take 33 T2 catalysts to take this vindi down. Dropable modules of 612M isk or more and this becomes profitable, given n exact 50% of the value is dropped. With 2 pith A, this looks profitable in 3/4 cases.
If we take a vindicator with dual PithA, a DC II, a cloak, MWD, and the rest LSE or bulks, it looks like we have a shot.. According to this spreadsheet, it would take 30 T2 catalysts to take this vindi down. Dropable modules of 556M isk or more and this becomes profitable, given n exact 50% of the value is dropped. With 2 pith A, this looks profitable in 3/4 cases. The cloak and PWD don't factor into the profitability, but I've seen some pilots talk about success with the cloak + mwd trick. I've never tried it.
If you're always doing cloak+MWD, you'll never get scanned, but scouts will spot that as odd activity in the common gank spots and may prepare for your arrival more than they'd do with an equiv tanked freighter or orca. They might also bump you until they can get a scan and decide.
So by the looks of it, it's not harder to take down a brick tanked vindi than a brick tanked freighter, so I wouldn't count on a lack of prepared fleets to save you. Then again, if the majority of fleets are designed to take down cargo expanded freighters, that's only like 18 catalysts. They'd need enough machs to bump you while they ping for more.
It's possible you could respond by fighting, but you've sacrificed your utilities for tank and have no webs or sebos, so that's not likely to go well.
I am a wall of text poster, but I wanted to put my thinking out there The answer really seems to be that you can't have the PithAs while you travel. Maybe a single pith A, but the gankers may be willing to roll the dice on that. The cloak invis trick flags you as worth investigating to the scouts.
Given all of this, what is the most common way to transport the expensive modules? Red frog is obviously not going ot be fast enough to get you there by the time you want to run without costing a lot, but maybe to get them out of Jita at least? What about an Insta-align frigate like a 15k ehp 1.9s astero? Thats easier to kill than a vindi for sure. If you can catch it. With covert cloak and 1.9s align, I don't see that as possible other than on an undock or dock, but scouting should be done for instas to mitgate that I guess.
