Solar Battery Charger ??

I would get 100 watts minimum for the effort. Also need a controller.
Verify that the chassis battery will also maintain the house battery... many will not.

$120 watts $100 But shop local and avoid shipping.

I have a 12 volt, 12 watt panel from an auto store that I use to help maintain the battery on a little used van. The problem is the van is often used only once a week and gets about two starts and 15 minutes of engine run time. The solar panel isn't able to recharge the battery. I doubt it can even cover the 0.5 amp parasytic draw.

Someone gave me a very nice looking 7.5 watt solar panel in a nice case. It would fit nicely on a dashboard. I tried it on a lawnmower battery which had 12.47 volts, no load. The panel was 16.1 volts no load. When the panel was connected to the battery the Voltage remained at 12.47. A current of 6 mA flowed into the battery. Would that be enough to maintain its charge? It is a bright but cloudy day; no doubt the panel would do better on a sunny day. But could it push 7.5 watts into a 12 volt battery?

The 100 watt Renogy panel and Renogy controller do a great job on the house batteries in our motorhome. The panel has a no load voltage over 20.
I think the panel would have to have a charge controller to prevent overcharging a battery.

JoeH wrote:
We store our unit under a covered storage spot. ... a solar charger that I could mount to the roof of the building

Instead of being permanently mounted, you could use a panel with a pole mount .
Did that with a Renogy 100 Watts 12 Volts monocrystalline panel. Easy to setup and also to rotate to get maximum sunlight.

I have a 120 watt panel that charges my batteries and also have a battery cutoff switch to isolate them and remove any parasitic draws. I bought mine at solarblvd.com

Yep. They didn't specify MH type and vintage. They said "chassis battery" though.

OP did not specify his RV type. Any modern Motor home may well be drawing an amp or more off the battery bank when stored. That is 24 Amps in any 24 hour period. It would take at least a 100W panel to ensure batteries are kept up properly .... assuming long nights and cloudy days occur.

We use a 35 watt panel for DW's car for the 6 to 8 months we travel.

Any 5W solar charger from Amazon will do. Something like This. Unless your MH has really a lot of things running and draining the energy when stored. My truck is old, when engine stops - everything in the cabin is off. I've seen people running the fridge in storage, this would require a bit more than 5W charger.

Disconnected chassis battery in a good shape doesn't need trickle-charging when stored 4-5 weeks or less.

Home Depot currently has a high quality 100W polycrystalline panel on sale for $109. With free shipping. Sale ends Aug. 31.

Amazon, other online stores, Home Depot (maybe)