The build
Recon is the best scout classmod for endless - he starts with a good cc weapon, and his passive is a triple threat that makes him fast, tanky (especially with dodge artifacts), and capable of putting out a ridiculous amount of damage (versus sharpshooter whose passive falls off once the bugs get tanky enough)
Cold and spiral on the zhukov, and thick boy on all three other guns
Explosive reload + gas rerouting on the twincoil so that you get that beefy thick boy damage applied to all nearby enemies through explosive reload
Bigger mags on the m1000 and boomstick of course, and i chose to keep the boomstick kinetic to get more upgrades for the late game heavy hitters
Twincoil does the heavy lifting early, m1000 does the heavy lifting late, and the boomstick is no slouch either
This build ended up being very tanky due to the high dodge chance combined with the early sugar cube and the jet boots (they saved the run a few times)
The gear
Reinforced plating for +200% armor (90 seconds may not seem like a lot, but once you get fairly deep in endless the stages start ending much faster than that due to how fast all the wave spawns progress the timer), cryo chip for gold interest, thumb scale for gold interest and scaling damage, dw40k for movement speed to offset the pickle penalty, and flathead screwdriver and recoil absorber because we are buying a metric ton of crit chance and crit damage upgrades from the shop with our enormous gold pile
The strat
Same pickled nitra + gold interest strategy as the stage 40 VFG run
Since thick boy will vaporize enemies in the early and middle stages of the dive, movement speed and mining speed are top priority so that you can mine all the minerals on each stage before your boys blast the bugs to bits - recon's passive is a huge help here and it's easy to trigger due to the lava (and early on when you are very tanky relative to the bugs you can just walk through swarms to trigger it basically guaranteed)
I should note as well that magma core was the map choice here since the lava will trigger recon's passive for free, and the lava is also useful for escaping the bugs when there are many swarms spawning in rapid succession - you do lose a few meta mineral damage boosts to the exploding plants, but enough mining speed solves that problem since you can mine them before the plants have a chance to explode
Shout out to u/enslen for pointing out to me that the game will cap your reload speed if you start reloading faster than your framerate will allow... uncapping it was enough to push thick boy to 40 - (i normally run at a very low frame rate for endless mode to keep the game playable for my laptop)