Most likely is a weak battery that's well on it way to dying.
Batteries lose some of the their charge when they are sitting idle. The longer they sit idle, the smaller the remaining charge. The fact the engine is easier to start after being run recently versus sitting idle for a longer period is indicative.
You may also have a parasitic battery drain. Try disconnecting the battery's negative (ground) cable when it's going to be unused for awhile. If the result is an easier to start engine, then I'd suspect a parasitic drain.
A quality multi-stage battery charger/maintainer would be a good idea, regardless of whether you replace the battery or not. The charger will keep the battery fully charged (unless the battery is tango uniform) and make it easier to start the engine. It will also counter any parasitic drain.
Note: Multi-stage charger/maintainers also keep the battery warm in significantly cold ambient temperatures ... that's what I have used for decades to make sure my vehicles start in -30 to -40 degrees F. (Whenever I encounter a battery heat pad or blanket, I rip it out and throw it away ... a drained battery is a drained battery, even if it's not as cold.)
Warning: Do NOT put a battery charger on a frozen battery. There is a distinct possibility doing so will cause an explosion. (When I worked at CarQuest, at least once every winter someone would come in with a battery that had clearly exploded.)
It's noteworthy that you considered a flooded engine. It's a common situation on engines with carburetors and especially Dodge big blocks. Most people aren't aware of this due to the proliferation of fuel injection systems, unlike decades ago.
Your motorhome definitely has a fuel pump ... there must be some way for fuel to get from the tank to the engine. (The carburetor -- or fuel injection -- cannot draw fuel from the tank. There are exceptions on some, especially small, engines but this doesn't apply in your case.)
Most likely, you have a mechanical fuel pump on the side of your engine. Alternatively, a previous owner may have replaced the mechanical pump with an electrical pump, ideally located close to the tank.
A possibility is a small air leak in the fuel line between the tank and pump. This would allow the tank to siphon fuel out of the line and back into the tank. (Mechanical fuel pumps on the engine suck ... both in terms of operation and application. Electrical fuel pumps, mounted close to or in the tank, push fuel to the carburetor or fuel injection system.)
However, I would first make sure your battery is good and fully charged. Likewise, I would make sure your electrical cables, wires, and connections are in good condition. (Especially, all connections are clean and tight.) Significantly, many people overlook the negative (ground) cables and connections.
Ballast resistors will NOT make an engine hard to start ... they're not part of the engine's START circuit. Instead, a failed ballast resistor will merely prevent an engine from running when you release the key to the RUN position. (The fact the START circuit bypasses the ballast resistor actually make it easier to start the engine ... bypassing the ballast resistor results in a hotter spark, which is necessary for starting an engine, especially when it's cold.)
Finally, there's no reason to replace a working ballast resistor. They are simple devices and either work or don't.
