The price sounds OK, since that is around rock bottom for a working Class A, but it's going to be crowded for 4!
Check the manufacture dates on the tires - it's stamped on the sidewalls. See the rvforum.net glossary under Tires if you don't know how to read tire dates (it's easy). You do not want to travel on tires that are approaching 7 years old, regardless of how good they may look. A 7 year old tire will fail at any instant, usually the most inconveneint and expensive one. It's not just a matter of convenience either - when a tire fails catastrophically (delaminates) at highway speeds, it can damage the RV severely. And if it is a front tire you could lose control. Don't gamble on old tires!
Tires have a life that is independent of mileage and that life is pretty consistently about 7 years. The chemical compounds used to keep the ruber flexible gradually evaporate , the tire gets stiff and the plies & belts begin to separate internally. The tire looks good but it can fly apart at any moment, usually when the tire heats up while drivingon a hot summer day.
You should also get the Rv weighed as soon as practical so you can determine the correct tire inflation pressure. Tire pressures are critical in avoiding tire failures on RVs. You can get away with incorrectpressures on a relatively light passenger car, but a heavy RV is unforgiving!