I can't really say much about positive about things to see and do along I-20, even though I am originally from western Louisiana (and live here again) and spent 5 years back in the late 80's and early 90's living in Birmingham, AL so drove back and forth down I-20 a good bit during those years. The Vicksburg battlefield park is good for a few hours (thousands of stone marker monuments for troop locations, memorials for each state that sent troops there, the largest is a pantheon like dome room, others are obelisk or columns or even statues, etc.), but is a drive through park with cell phone audio tour and not suited for large motorhomes (25-30 ft motorhome maybe, 40 ft I doubt it), and probably not worth renting a car just to drive through unless you are a big civil war battlefield enthusiast. Culturally speaking north Louisiana is very different from south Louisiana, and the Duck Dynasty like culture is a good part of it, my grew up in NE Louisiana about 65 miles from Monroe, and I have ancestors that settled in that region over 300 years ago. A site I don't suggest visiting in the area is Poverty Point, even though it is a world heritage site, as there is just not much to see there, beyond a some ripples in the ground where ancient irrigation mounts where thousands of years ago. Going on across I-20 be aware some of the worst pavement that RV'er report in the US is on I-20 just east of Shreveport, though thankfully the state has announced plans to start repairing this section of road, unfortunately this is not likely to be done by the time of your trip. Going west into Texas I-20 is ok, but again not a lot to spark interest in stopping along the route, other than maybe stopping for BBQ in Kilgore at Bodacious Bar-B-Que (original location, they now have about a dozen locations through east Texas). Not necessarily the best BBQ in Texas, but probably in the top 50, maybe even the top 20, but being located at an exit on I-20 with a large parking lot (truckers stop here) it is probably worth trying. Another interesting stop on I-20 further west, is the Frontier Texas Museum in Abeline (RV parking questionable depending on how full the parking lot is). Consider stopping at Cline Corners travel stop between Carlsbard and Santa Fe at I-40, it is hard to describe, other than a gas station gift shop, that grew, and grew, and grew over the last 50+ years, where you can buy anything from cowboy boots to fudge. Speaking of gas stations while in Texas, make sure and stop at one of the large Buc-ee's gas stations with 100+ fuel pumps, complete with a fresh made BBQ island, made to order food, dozens of fountain drink dispensers, countless amount of road snack food and some of the cleanest restrooms you will ever see in a gas station.
Going along points west on I-40 there is Petrified Forest national park, worth doing, but be aware the pavement on park road at least in the southern part of the park is awful, teeth jarring awful, as of 4 months ago. Another stop heading west is Meteor crater, which is good for an hour or two if you opt to do the 1/2 mile (maybe 1 mile) hourly guided rim walking tour.
I will leave it there until I hear more about where and for how long you plan to stop in AZ, UT, CO, etc.