I've partied there many times with gals for one, two, and even three nights in a row.
If I had them to do over, I'd get more sleep, drink and eat less, do more exercises, and attend more shows.
Have fun.
Not an MH member, and too damned timid to even try on commercial, so kudos to you for giving it serious thought.
Redeye flights would lessen the risk. Took one last week with ~60 on the manifest (had to ask, it was so empty) for a ~300 seat international flight. Entire rows were empty. If you couple that with people sleeping then your chances to get busy undetected are fairly good.
Don't know about you, but there's no way anyone other than me will fit into an aircraft lavatory unless they're short enough to stand on the toilet seat. Even then my shoulders will be hitting them as I close the door - damn rooms are small nowadays for economy sections. Perhaps the business or first class lavs are larger? You could recon with an earlier flight; just book an economy seat but check out the other lavs during boarding or deplaning, then decide if an upgraded seat is worth it.
Getting busy in the seats gives more room but less privacy. How quick can you nut, and is it all about you getting off or does her O figure into that time as well? Airplane blankets are a bit small for what you'd want to cover up, so consider taking several with you from the recon flight, sew them together, then take them onto your MH flight. Might want to practice ahead of time. If crew spots you they'll know what's going on, but may not care if you're discreet. Tips ahead of time might buy some extra tolerance.
BJ in the seats is an easy one, just throw a blanket over top and keep your eyes peeled for bypassers. If she needs to stop then work out that signal ahead of time and no, it's not when you put your hand on her head! Ever seen what that looks like? I have, and there's little doubt he was getting a hummer in the seats - gave him a thumb's up and kept walking.
HJ is the easiest since both can keep a lookout while everything is under a blanket. Pretend you're in high school at your girlfriend's house watching TV and the parents are in the next room; kinda the same thing.
Decide ahead of time how you want to clean up afterward, and for fucks sake don't leave a mess behind! Someone else is going to be using that plane after you.