Craigslist is better. Often the units on the RVT are sold and very few in number. At least it was that way for a class C.
The best way to determine pricing on used units is to know what the NADA guide says the RV is worth. That is using the low retail price with a mileage adder or subtraction and no other added options, even if the rig has them. You know if buying from a dealer that they paid less than that number. Check with your bank or credit union and ask how they value used RVs. Even if you are paying cash, it is an excellent negotiating tool to use the argument that my bank will only loan $X. The dealer doesn't have to know how you are paying for it until after the negotiations are done. They may counter with the argument that they can get you financing but I always counter with, "I prefer to finance with my CU". It also doesn't hurt to spend some time on CL going way back and seeing how long particular units are on there. That should tell you that the asking price is too high.