Just to be certain, make sure his battery is 100%. I was chasing a loss of power for a while before I realized my battery was on it's way out. I put a new battery in and there was a noticeable difference in how my ski ran.
Rubber all the way, I have had issues with the aluminum ones coming loose as well. Truth is, the OEM impeller does not have a seal, I'm not 100% convinced they are necessary and have run both Solas and Skat impellers without them and didn't notice a difference.
I found this pic of a ProTec pipe in a freak, not sure what model but this area will give you trouble just getting the chamber in. The dry pipe chamber is bigger all around so say goodbye to your hoodseal.
I highly doubt you will fit a traditional dry pipe in the hull, there's more to it than just hood liner height (which is probably the easiest issue to solve).
The engine bay opening beside and behind the chamber has to be looked at and the distance to the bulkhead/rear of topdeck may be an issue...