In general we recommend buying used, especially for your first or second RV. On a used RV, somebody else takes the big depreciation hit and you can later trade it for the one you really want without a big loss. But with a small pop-up, the depreciation dollar loss is not as great as with a Class A, for example, so a new one is less of a financial risk. As you go up in size (and price) to the larger pop-ups and hybrids, then the 30% or so first year depreciation becomes a more significant factor.
People are upgrading their RVs all the time, or finding out they don't use it much after the first summer, so there are lots of lightly used RVs around if you are willing to take the time to look. Private sales are an excellent source - prices should be well below the dealers. The intial asking price probably won't be, but don't be afraid to make a low offer. Use the NADA RV guide (www.nadaguides.com) as price guide and don't pay more than the low retail figure (and nothing added for options either).