Lots of good suggestions above, they covered most everything.
Reducing that noise is mostly doing little bits, making every area as good as you can.
You didn't mention the age or engine in your motorhome?
Many are known to break manifold studs, or crack exhaust manifolds. Exhaust leaks = extra noise.
Some, particularly early Ford V10's, sometime blew out sparkplugs. A v10 running on 9 with an open hole would be very noisy.
Fan clutch... Your engine fan should have a good functional thermal clutch. You'll hear the fan when the clutch engages, which will be when you are working her hard and the temp rises a bit. If you hear the fan all the time, a new clutch will quiet things considerably.
And finally... the '99 V10 we used to have was horribly noisy. It also was extremely rpm happy, downshifting and reving high at the sight of a hill in the distance. I put in a tuner from Brazel's, and the difference was AMAZING! More power, better torque at low rpm, and no more downshifting. She'd hold in high gear much longer, and keep the rpms lower much of the time. This made a huge difference.
Then I fixed it for good. Traded for a DP.