To select the right inverter, you will need to decide how much power you will require. You can calculate this by adding up the consumption (watts) of all the devices you will power at the same time. Then add a 20% to 30% to that as a safety factor. The cheapest inverters are modified sine wave inverters, but I would suggest you
not purchase one of these. I would recommend a full sine wave inverter, especially if you are using electronic devices like a TV. Like most things, lower price can equate to lower quality/longevity.
Installation difficulty can range widely. It can be as simple as installing the inverter and using extension cords to power your devices to as complex as installing transfer switches to switch the power to the outlets between shore power and the inverter as necessary.
You might want to spend some time on Youtube to see what others have done. Though not specific to RV's "DIY Solar Power with Will Prowse" on Youtube can be very helpful. Some of Will's early videos were from when he was using solar when he was living in an RV. Later videos are more geared to large scale solar builds.
Hope that helps.
https://www.youtube.com/@WillProwse