Late April Euro Roadtrip

[Lugy]

Evening folks, the OH and I planning on doing a week long road trip at the end of next month. We'll be on the continent from 1st thing Monday to last thing Friday (we need to travel to Dover from Edinburgh so that's a day before and after taken out!). We'd like to visit Belguim properly (apparently stopping in services wasn't enough last time) and maybe venture into Germany to visit the 'Ring.
Can anyone recommend places to visit in this area?
Ideally we'd like to camp to keep costs low but will it be warm enough in the end of April?