I'm sure 2 layers of PnS would be double the soundproofing. I don't see that it would cause any issues. When I installed mine I just laid it right over the hump and then cut around the edge so I could remove the hump when I wanted to. Did the same thing with my EZ Cool insulation.
1970 F100 Sport Custom Limited LWB, 302cid, 3 on the tree. NO A/C, NO P/S, NO P/B. Currently in 1000 pcs while rebuilding. Project thread: viewtopic.php?f=22&t=59995
Plan: 351w, C4, LSD, pwr front disc, p/s, a/c, bucket seats, new interior and paint.
1964 Ford Fairlane 500. 289/Cruise-O-Matic, A/C, P/S.