Seamless looping of ambient reverb-heavy tracks?

[Rogar]

Hello, Mixcraft wizards!

I need to seamlessly loop reverb-heavy but very quiet ambient tracks (because of a request from a talented game developer who wants to use my old tracks in that style for his upcoming game).

Do any of you know how to do this with synths/VST sounds like ambient pads (especially bass-heavy stuff like "warm pads" or drones)?

Also, this unfortunately needs to be done in mixed-down audio files (.wav or .ogg), not just within the DAW itself (where it's very easy to loop drones/pads endlessly because of tricks like crossfading or reversing audio, but I need to actually mix down the files first, and work out a loop in those).

I am not that experienced with this, but so far making seamless loops with sharper attack instrumentation or a lot of percussion or "hits" tends to be no prob to loop seamlessly, but I haven't been able to get that to work with pads/drones:

The "top and tail" method (where I duplicate the MIDI data in the DAW, and then excise the middle portion for the looped part that has the reverb tail mixed into the beginning) with manually applied tiny-as-possible fades (usually between 2.5-4 milliseconds) at start+end of the loop is the method that's worked optimally for me sometimes, but I'm usually reliant on orchestrating something with a sharper "attack", even if it's still quiet (like harps / zither / acoustic guitars, and sometimes flutes).
I can't get it to work with stuff like pads and drones...
(And stuff with more percussion / "hits" would also work, but that's totally out of synch with the style of this current project I'm working on, since the developer wants quiet heavily ambient and "ethereal" sounding tracks, but he still wants seamless loops...)

When I've tried to make an audio mixdown of something that start with bass-heavy ambient pads, those methods don't cut it because tiny fades that are too short leave that pop/click sound from unequal amplitudes at the loop point, vs tiny fades that are a little too long create that audio impression of an unnatural "jump" that doesn't sound seamless enough.

Do any of you know some way to engineer tracks to leave the core composition intact but somehow get equal amplitude at the start and end points of each loop, without having to manually apply fades to force a zero-crossing point?