Patten I think you may be under the impression that there is a "structural layer" of material on the other side of the headliner where you can attach handrails. There is not. The only "structural layer" is the deck itself....hence the answer you received from(and his misunderstanding of your question) willpep. The only load bearing member is the deck. So If you are going to install handrails, they will need to be thru bolted to the deck as willpep did. That or attach another structural member where you can attach your handrails. In any event, you are going thru the deck.
With that said, headliners are something that witches and devils design. If you mess with it, you are likely to regret it as it may never go back the way it was. LIke someone said, it is "destructive". Call it superstition or whatever, if my headliner is in good shape, I DO NOT MESS WITH IT. It will haunt you.
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B