Generally if you hear the solenoid 'clunk', it means the starter motor has an issue. RVs set so much, the brushes in the starter motor can get sticky in their holders and that, with a little dirt, can prevent the motor from running. The nice thing about gas Class As is that they set up high enough that sliding under to do stuff is easy. Using an expendable screwdriver to short across the 2 big terminals on the starter solenoid will bypass the solenoid contacts and deliver the 12 volts straight to the starter brushes. If the starter then cranks, the brushes are OK and the solenoid is at fault. If not, it's the aforementioned brush issue. Since starters began using permanent magnets, working on them has become a PITA. If the brushes are the issue, you CAN clean and fix them but be prepared to use all of your vocabulary. I'd just spring for another starter.