The installation instructions state that you should tighten the mounting bolts evenly, using a technique like tightening lug bolts on a tire, until the gasket is compressed by about 50%. 40-50 ft/lbs. would be excessive. I'm guessing it's going to be something less than 10 ft/lbs; probably a lot less.
That sounds a bit high - they should be nicely snug but not overly tightened. The idea is to compress the gasket a little but not to squeeze it flat or cause it to squish out the sides. If the a/c manufacturer doesn't provide a torque spec, "snug" is about as definitive as it gets.
Check the tightness again after the first trip and again in another month. The bolts sometimes loosen up a bit.