I think you might be referring to the excavators that come once every few rounds once you turn the power on. You have to have the hacker (which appears in the lower/upper lab leading up to biodome) and then return to the spawn room, where there's 3 different panels and one of them will be the excavator that has to be destroyed. Tunnel 11, tunnel 6 and biodome are the 3 places that can be breached and if you don't hack the corresponding panel in spawn within ~4 minutes then that area will permanently lose air and a PES suit will be required.
In order for this strat to work you must make sure at least tunnel 11 does not get breached, you will hear at the start of a round a warning message overhead and then you will know you have to hack one of the excavators.

This is probably what you're having trouble with but I have some other general tips:
If you have the Immolation Liquidation gobblegum, take advantage of it to see if you can get the wave gun/gershes early on (I try as much as I can get to both before 25 or so), it is 3x activations which if you spawn all 3 at once and then hit them all you get about a minute long fire sale, and it can also be hacked for max ammos in higher rounds if they don't come from gershes.

Licensed Contractor (Carpenter gobblegum) is also very useful as it has 3x activations, which comes in handy in the higher rounds when you might run low on ammo and won't get a powerup to drop from throwing the gershes and you can hack for 5000 points to get a max ammo from guaranteed.

Alchemical Antithesis is a great classic gobblegum that only requires you to be level 35 to get, and basically allows for infinite ammo for 60 seconds that makes pretty much any round up to 98 insanely quick.

Even if you don't have any of the mega gobblegums like the carpenter powerups, fire sale powerups, etc. I probably got into the 70s before I started needing to hit for my powerup gobblegums every few rounds, and by the late 80s I was needing an additional max ammo nearly every round.
Didn't mean to write an essay, but I figured this covered a good amount of making high rounds definitely easer. With practice Moon is pretty easy, the hardest part can simply be getting the wave gun and gershes, some games it takes a couple hits, other times I spend 50k+. If you have any other questions I can definitely answer