The only agent I've seen doing packages is travel destinations.
https://traveldestinations.co.uk/acc...u-rouge-spa24/
The campsite,
https://en.eaurouge.nl/contact/route which you could book yourself is just off the old circuit, almost down at Stavelot. It's claimed to be a 20 minute walk, but probably nearer 40, and that's only to the bottom end of the circuit. It is possible to drive in and park closer.
Cheap & cheerful is diy and camping on-circuit, campsite P2-6? - atmosphere aplenty. (If you're a le Mans veteran you'll know what that means).
edit - found this resource
http://www.lemans-www.com/Info-Spa-Camps.html , disclaimer - have not read any of it yet