Yes. It is allowed to park and stay with a motorhome or a vehicle with trailer in the area located in Joan Fuster Avenue, between Salou-PortAventura train station and Sol Costa Daurada Hotel.
Further information: Where to park
Furthermore, you can stay with your motorhome at any of two campsites of the city:
Camping & Resort Sangulí Salou 1a
La Siesta Salou Resort & Camping 2a