Schroth Harnesses for the M5 (these connect to the rear seat). These use existing mounting points and do not require drilling. They also do not interfere with use of the regular seat-belt. Access to the rear seat is not hindered in any way, because you can unclip the rear belt when not in use, and just clip it back when you want to use it.
These harnesses cost $150, but I am selling my set for $80 (plus shipping). I am selling because I have a roll-bar installed with new 6-point harnesses.
Photos:
Please PM or e-mail me with any questions.
Thanks,
Daniel