Hinged seats aren't really gonna matter in a Boxster like they do in a 911. PCA says IF you have roll bar, you MUST have harnesses. And if you have harnesses you MUST have head and neck restraint (aka HANS or similar - I personally like the Flex by Schroth). And to that point, restraints must be equal for driver and passenger for DE... i.e you cannot wear a harness but passenger (instructor or student) only use 3pt. My DE car has buckets, 'harness' bar and harnesses. If I take a student out who doesn't have a HANS, then neither of us can wear my harnesses, we MUST use OEM 3pt. In which case I grab my other helmet and wear my Simpson Hybrid S (which I use w/ intro/intermediate students as MOST do not have harnesses... and I ain't sitting right seat w/ out it!).
So, back to as @iancole said, it depends. Figure out what exactly you
want to do and
who you plan to drive w/. Then build a system which complies and allows for some expansion.
PS - IF you add harnesses, don't buy garbage seat belt "cancellers" off eBay/amazon. Buy real DOT standard seatbelt extenders and just cut off the extra receptacles (leave webbing attached to tongue portion for easy grabbing). Garbage ones break easily and fishing broken pieces out would be a real PITA... I narrowly dodged a bullet when a student accidentally snapped on one of mine getting in the car. Luckily w/ some Gorilla tape and a steady head I had enough 'meat' left on the bone to extract easily.
https://www.seatbeltextenderpros.com/porsche-boxster-seat-belt-extender/
(regular 7" is what I use)
Threaded Mode
