Solar wattage needed depends on how many watt hours you burn and is a function of how many amp hours of battery you have. So it’s inappropriate to give a simple number. But I can give you some guidance based upon some assumptions, which you will have to fine tune yourself.
If you just have a single 80 amp hour battery as most TTs come off the lot with, AND that serves you well for a day, AND You use no more than the 40 amp hours recommended overnight, then a single 100 watt solar panel will suffice, PROVIDED You get a full day of bright sunshine, and use an MPPT charge controller.
To keep that battery fully charged on a cloudy day, you might want two 100 watt panels. If you have a pair of those same batteries, you will probably want 3 - 100 watt panels. If you have a Class A motorhome with a battery bank that runs to 600 amp hours, and you use them to capacity, think something like 600 to 800 watts of solar.
I would suggest that such estimates are very much dependent on how much power you use. So my suggestions above are highly dependent on your usage as well as my assumptions.
