Very nice country & people, worth visiting.
Had 4 months last summer Germany / Poland via Mosel & Rhine, black forest, Bavaria, Prague & into Poland, wild camped many times as very few campsites, only used sites for water etc a few nice sites but some are very dilapidated!*
Best to stay at sites for Warsaw, krakow, which are worth visiting.
I visited auschwitz (you can o/n in the parking area) & many other camps, also salt mines, wolfs lair, schindlers factory, the lakes area, border with Russia, all the Baltic coast & much more.
There are many supermarkets many are tescos which I used.
A data card is very very cheap for your phone / laptop.
If u have refillable gas bottles LPG is everywhere.
Most main roads are pretty good, but go of the beaten track & they can be very very bad with BIG potholes etc.
Hope that helps
Regards Ian*