ohm i love that 3 enterance cave system.
i play as medic, lvl 3 atm. had to solo 100+ specimins 3-4 times already. lots of fun kiting em around there. I only ever duck into the house to buy, or grab some ammo in the first room if i run out of respawns by the lake, chopper and wherever else outside.
Same here, just as a berserker.
The easiest way to get around on this map for me is to wait near the hut, kill as much as possible and when things start to get ugly (Fleshpound or just too many smaller specimen to kill until they surround you) move towards the cave entrance where the trader hides behind a rock. Shoot while retreating and you can gun down a lot of them already.
Once you are inside the caves, timing becomes important. You have to move through the caves quickly or they will surround you. You also do not want too many of them clogging up the cave entrance or some might turn around and become a problem later on. Try to kill as many of them as possible. You will get a feeling for the safe amount of time you can stay at the entrance once you did this a couple of times.
Either way, you want to head to the exit near the helicopter as fast as possible. Once you are there, kill any specimen that are approaching from the outside (watch out, there's a spawn directly behind the helicopter), turn around and open fire. Give them everything you've got. Once you killed them/they closed in, move towards the mansion but do not (!) enter it. Turn left and head towards the small hut again. Gun down any specimen you can find on the way, but do not stop. The tricky thing here is you do not want to be too fast either, or any remaining specimen in the cave will turn around and become a problem on the second run.
Once you reach the hut, repeat the whole process.
I managed to reach the Patriarch in a 6-player game pretty much on my own this way. The other 5 initially tended to defend either the mansion or the cave leading to the mansion and got killed. Later on we went my route together but did not manage to kill the Patriarch.
Important sidenote: This is pretty obvious but if you want to be able to pull this off as a group, be sure to stick together. If your team splits up chances are high that you will be intercepted in the caves. This will prove deadly in later waves.