IMO everyone who owns an RV should own a multimeter. Even <$10 units from Harbor Freight or Amazon can still be used for basic diagnostics, even if you have no idea how the sparkles work their magic. Go buy one and make the following measurements:
1. Measure the voltage across your battery (multimeter in voltage mode, DC, black wire to battery ground, red wire to battery positive) when you "think" it's fully charged.
2. Measure same when you think it has died.
3. Measure same when you think you are hooked up to a decent charging option like shore power (NOT your tow vehicle).
4. If you believe you have solar installed, measure same when the sun is high and hot, and your panels have no shade on them from trees.
Those four measurements will tell the rest of us a lot to help give you pointers on things to look at. It will cover and/or rule out various things like problems with your charger, whether your solar is actually working, etc.
If you are using an entirely stock system, if it is anything like our Milestone 386BH, you should know it's woefully under-powered. We had a single lead-acid 12V battery, a 30W solar panel on the roof, and a low-end PWM charge controller that wasn't even working because its fuse wasn't even installed. This was connected to a barely-adequate (but surprisingly - a quality manufacturer) inverter hooked to our fridge. With the setup as it was configured, it was barely able to run the fridge for 4-5 hours. That's just barely enough to haul from one campsite with full power to another, but not much more. All these problems are addressable (probably with a bit of $...) but before we guess what your issue is, let's get some data to really understand the root cause.
I don't specifically advocate this product but for $14 this is a great buy, it's tiny, does about everything an RV owner might want, and if you have Prime you can probably get it tomorrow if you are in their delivery radius: