I bought the doublewide next door to rent out.

Sounds like PEX tubing.

I've never seen a mobile home with PEX in it (unless they re using it in the
NEW ones)
I have seen polybutylene (PB) grey and CPVC cream colored. Since its
crimped, I'm guessing PB.

If I was 'adding' to a PB system, I'd go with PEX ( red, blue or cloudy
'milk jug' colored plastic)
Cut in a "T" to the existing line and away you go. You can rent the
crimping tool and get all the PEX and fittings at Home Depot.