Tim H16,
This works for me (and I'm 60 now & right at 200#--slim & trim according to the significant other . .
):1) I use a DaKine windsurfing harness w/ flotation and a reinforced seat & lower back stiffener. I solo my H16s regularly and spend lots of time on the wire.
2) My trap is fully adjustable when loaded (through about 24", or horizontal to almost vertical). I sometimes stand well forward when solo (a lot like windsurfing or true surfing when the wind is up!). This length of adjustment also allows me to reduce 'tailbone load' when I'm (not often) on the rail or corner post.
3) Last trick: I have aboard a 12" square of approx 1" closed cell foam (cut from an old camping mattress). I tied a 1/4" leader through a hole in one corner and allowed enough slack to reach midway up the rails. Makes a nice cushion (and the SO likes when she's aboard) and it's always there when I want it.
Good luck! us old salts have to take care of the boney places!