There is probably a level of hell built around cross-country road trips with Robin Williams. So it’s quite a surprise that RV, in which Williams treks from L.A. to Boulder with his wife and kids, isn’t actively painful to watch. Thankfully, he plays it relatively straight, sparing the world from yet another round of his trademark gibbering, in favor of aping the hapless but earnest Clark Griswold of the Vacation films, RV‘s obvious source material. The result is a workmanlike family comedy with enough pratfalls and poo jokes for tykes and enough sentimentality for parents (Williams still pours the schmaltz with a heavy hand). Add a few points for the funny and foxy Cheryl Hines (Curb Your Enthusiasm) in the wife role and Jeff Daniels as a roving redneck. Then take the points back for director Barry Sonnenfeld’s decision to film his American road movie . . . in Canada.