Hi one of the most common electrical
problems for RV's is the lack of a suitable ground. Dimming or blinking light
is a very good indicator of this problem. Next, are your battery connections clean and tight? Don't just wiggle them! Get rid of all the pretty green stuff. Tinned connectors are less prone to corrosion than brass or copper. Don't mix metals if possible, you really don't need a mini battery happening on your terminals!!
First thing I would check is the battery negative to chassis ground. Don't just look at it! Physically remove and thoroughly clean all metal parts and lightly grease everything with axle
grease before reassembling things Star washers are a wonderful thing. Messy but necessary for your peace of mind.
If this does not do the trick, and it uusually does, then open up every connection and for best results solder them! Failing that separate them, clean and reassemble using die-electric grease and heat shrink tubing.
Sounds like a lot of effort? it is, and that is why the manufacturer doesn't bother. You reward for all this work is good lighting
both inside and out plus the knowledge that you'll never have to this again.