European trucks have usually exhaust under chassis and even many showtrucks here have exhaust under chassis. Then there is sidepipes too, technically they are under chassis too. So in that build with that set up i would use sidepipes.
Here is example how good they can look in showtruck. This Volvo is actually daily workhorse and it hauls some fine Finnish beer around our country
If youre not familiar with Juha Ristimaa`s trucks just google " Juha Ristimaa " He has website too for his company, but there update progress coming so i guess he has something new to show us again