Blackout curtains are a good solution, plus they add extra insulation over the windows.
Try playing white noise at night. There are special machines for this purpose, but you can also play these noises from your phone.
Power down any appliances or devices that might make noise during the night. Put phones on silent so you don't hear any dings in the middle of the night.
Not everyone has the money to buy a new RV mattress. Instead, try investing in a mattress topper.
Most devices emit blue light, which keeps your eyes and brain active even if you're trying to relax.
Weighted blankets are heavy enough to provide a full-body tactile experience. It helps you sink into the mattress and relax more easily.
Electric heaters or fans can help regulate the temperature so you don't need to use your A/C all night.
It can be helpful to get up and move before bed. Do some chores around the RV, stretch, and spend some time with other people.
It's hard to sleep in an RV if it's constantly shaking and settling throughout the night. Invest in stabilizer jacks and try to find a campsite that's fairly level.
Melatonin is the most common and easy-to-find option. Another popular option is CBD gummies. You can also try bedtime teas.