My typical situation online:
I build my NL10 $10 buy-in gradually to $30-$40 and then, eventually (~85% of the time), I lose it all to an all-in against another big stack. The longer I play, the more certain I will lose my stack to an all-in.

Whenever I build a big stack:
- I get very overconfident/cocky and take many risks (much looser play than normal)
- I relax and my concentration deteriorates
- I start to play very aggressively (that's fine in middle/late stages of tournaments but bad in the early-stages and in cash games)

Because this is a 'mental-leak' it requires a much more drastic solution than a typical 'playing leak', SO unless I have the stone-cold nuts:
1. Should I completely abstain from all-ins against other big stacks?
2. Never commit more than 20% of my deep-stack on any one hand? (if >= 1/3 of my stack gets in by the turn, I WILL be all-in by the river even with 'only' one-pair like a big overpair or ace TPTK)
3. Should I just "rathole" when I build big stack and then wait until the time-limit expires and then buy-in at the regular price?

I like #3 (ratholing) but I know it really pisses off other players, so they will take notes on me and playback at me later.

It's online, nobody will care about ratholing, and if they do there is nothing they can do about it. If people were really willing to put in the extra effort it would take to target you, they would be able to focus their energy on moving beyond NL10.

There are fundamental differences between full stack and deep stack play. Deep stack play is much more complex. The deeper effective stacks are, the more ways a hand can play out (or the larger the "decision tree" is), and the more expensive mistakes are.

For instance a hand might be a bet/shove on the flop with a shorter stack and a check/call with a deeper stack, because it has high equity against an opponent's range but plays poorly on most board runouts.

So ratholing is probably your most effective option, until you study deep stack play more and those spots where you currently make massive mistakes become +EV.

Isn't it a possibility that you are playing a high variance (losing) style that is just destined to lose eventually?

Let's say you make plays that work out 80%+ of the time and you keep picking up chips but when it fails you lose your whole stack.

Study pot control and try to limit playing hands over-aggressively vs other deep stacks when your in position

That's the main reason why you often see people build a huge stack in a short period of time only to lose it all in the matter of one or two hands.

Just the fact that somebody regularly sits on 3-4 buy-ins at an online table makes a high variance playing style very likely. I would estimate that happens significantly less than 10% (maybe less than 5%?) of the time to somebody who plays straight forward TAG poker for 2 hours.

Honestly, it sounds to me like you are just bad at poker and lose your stack when your aggression + luckboxing can't beat the nits anymore. I could be wrong of course, but this whole, "yeah I easily gouge out two or three BIs and then it goes wrong"' sounds like BS to me. If it's true, well then just win 2 BIs and quit.

Deep stack poker is different .. pot control, checking TPTK on the Turn, not committing to high variance draws.

How are you building your stack? Getting others to fold to shoves or at showdown?

Take a look at the hands you 'win' with and compare them to hands at the end. You are not that different with the emotional high that building a stack can give you and then opening up your range to the point where you get away from what actually did build your stack in the first place.

Cash is not tournament ... although it would be nice you aren't trying to get 'all' the chips.

So you 'cash n dash', big deal. Would you rather the players 'target' you with a min stack or when you have a 3-4x stack? GL

If your problem is that you start playing too loose and too aggressively with a big stack, perhaps the answer is try to force yourself to go the other way and tighten up. That doesn't mean that you should wait for the nuts, but it does mean that maybe you should avoid making the pot big on early streets.

Depending on the skill of your opponents, routinely getting it in with two pair while deep-stacked is problematic. Doing it with one pair is suicidal.