We have a 38' motor home and hardly ever stay in an RV park. As pointed out, the main consideration is being able to turn around and clearance. Also, what may work when dry might not work after a rain or snow. We tow a Jeep, so in the case of minor traction problems can help out the motor home. We find nice spots to park the motor home and then use the Jeep. I don't think I would want to try with a 40' or 42' with tag axle though. A diesel has a shorter turning radius than our Ford F-53, so maybe 40' or 42' would work as well.