[Daryles]

2005, if they used PEX plumbing, they used plastic joints. If there was any water in the lines and it froze the PEX is good but it's likely the plastic joint broke.
Once you take down the basement walls you will be able to decide which way to go.
If you do decide to replace the lines, you can use the old lines to pull the new lines through as long as ther isn't an elbow in there somewhere. You will need a PEX crimping tool and a bunch of elbows.
If you have the coroplast bottom down, you could route the new lines away from the outside and put pipe insulation on them to protect from freezing.
One of my future projects is to make a hot water loop from the water heater around underneath, through a water pump and back to the water heater. This would be a supplemental heat source for preventing pipes and freshwater tank from freezing.
Have a good look at the water heater for splits.
I know one of our members was successful having it welded vs replacing it.
Also replace the anti siphon vacuum breaker valve on the black tank flush system with a brass one. They leak.