You have run into the winter blues when it comes to solar mounted flat on a RV. Many people head for BLM land in AZ or other states for the winter and found that flat mounted panels in winter just will not produce enough output. Part of the reason I made half of my RV array tilt, at least I can tilt those enough to garner some output in winter. If you go on Youtube for people who went to Quartzsite in winter with flat mounted panels on their RV, they learned they needed to tilt panels or have some ground deployed panels tilted perpendicular to the sun which is low on the horizon.
For my house, I spent the extra money on a MT Solar tilting mount with the ability to tilt to 65 degrees in winter. The mount was costly to say the least with current materials' price increases. However, if one runs the numbers thru a calculator that determines solar output on azimuth and tilt at various latitudes, you will find that tilt in the winter months is very important and the return on cost might be worthwhile. What good is a solar array in winter if it doesn't produce? Adding size to arrays might help but still, if fixed angle, at some point you will lose productivity. If tilted to 60 degrees for winter output, then in summer, the output will decline. Maybe the answer for fixed tilt is to make the angle more conducive to winter output as there are more daylight hours during summer. The best solution really is adjustable tilt, although many will argue to simply add more PV but with limited space such as an RV, you can't do that.
