The recent thin Flex panels from many of the online purveyors, are not enduring very well when attached to an RV/Van roof and exposed to the elements. A framed panel with glass over the solar cells is much more durable, but of course is much more visible and takes more thought as to how to adhere/attach it safely.
The subject of solar panels and batteries in mobile applications is rather vast, and there is a lot of bad info on Youtube from the self important who do not understand the subject in which they are posturing themselves as proficient in.
What you need to power, and for how long, and whether you will be able to plug in to recharge now and then, all have huge bearings as to how much solar wattage you will need, as well as how much battery capacity you require. Also be aware that almost every single flooded/wet 12v battery which has 'deep cycle' listed on its sticker, is really only a dual purpose battery capable of achieving only half the total number of discharge cycles as a true deep cycle battery.
The only true flooded deep cycle 12v battery is the GC12 size group such as these:https://www.battsys.com/us-battery-us12vxz-group-gc12-batteryhttps://www.trojanbattery.com/product/t-1275/
The gc12 size are larger and taller than the regular biggest automotive jar battery available, the group 31. They do not have CCA ratings as they are not designed for engine starting. They will likely have enough gusto to start engines in mild temperatures, but they are too big to fit underhood anyway at ~11 inches tall, 7.5 wide and 13.5 inches long.
AGM batteries can be good 12v deep cycle batteries, but many are now built to a lower price point, intended to be Used as starter batteries, marketed to those who see higher prices and the letters 'AGM' as being far superior. AGM's are a bit more finicky on how they are recharged when deeply cycled. If their finicky nature is not catered to they will not do as well as flooded/wet cell batteries, in cyclic duty, and will cost 50% to 200% more for the privilage of dying earliier..
AGM batteries are NOT more resistant to abuse, and abuse can be considered not quickly being returned to full charge.
Achieving 'ideal' recharging, can be taken to ridiculous levels. Accepting shorter battery life and replacing more often can be quite a bit less expensive, in the short run, but reliability goes down, and battery retailers might only warranty the battery once, and if/when failure happens mid outing/road trip, it can be quite inconvenient forcing one to buy the first battery available, nullifying any of the initial savings.
In general the 'kits' sold, still require the end user acquire fuses and little bits and pieces to get a fully operational system, and the kit buyer winds up with a sub par system for more $$ than if they had bought better parts individually.
Wiring needs to be done properly, with proper crimping tools and adequate gauge wiring. If halfassed, one will simply have to do it over at some point at best, and at worst the van burns down, so doing it right the first time is paramount.