One big thing you've got going for you is that Berkshire is carried by RVDirect.com. Go there, select your model and options or select an in stock model, and request the price. Within a few minutes you will have a very good price, which you can use with your local dealers.
I just did this, yesterday and today, and completed a purchase of a Sunseeker Class C. Two dealers beat the RV Direct price, and the third came close. On the particular model I bought, if RVD's MSRP is to be believed, we got prices which were 38-40% off. I think that's on the high end of what might typically happen, because I think our model had a lot of fluff built into MSRP for some reason.
PS: They don't care if you are a cash buyer. In fact, they would rather finance you, and sometimes you'll get a lower price that way.