Tbh the early game isn't that bad. For the beginning you want to place down around some scavengers, but prioritize getting six shooters. If you can get one in each lane then you should be set against the helmet dudes. Six shooter will get overwhelmed if 2 helmet dudes or a helmet dudes + any other enemy spawn in the same lane so if that happens use some combination of waste bucket/shredder/mouse trap/glue mat to dispose them (whichever is cheapest for that situation).
Afterwards just try to get down as much scrap production as you can and try to get some 01 shredders down. You only need 1 in each lane with glue mat support (or 3 shredders if you use crossroad sign strats, which I suggest you do for this stage) and they basically defend everything, including vrms and matryoombas (although against matryoomba it can get overwhelmed without support). If you can get the 01 shredders down then you shouldn't struggle until the incinerators spawn, but by then your defense should be good enough to deal with those