Strad here are a few pics of how I did mine. Use stainless for sure. I did use PT wood.
Drilled a recess hole for the carriage bolt slightly undersized. Then I put 3M 5200 on the underside of bolt. Smack it in with a hammer and fill recess with more 5200. Put some masking tape over the 5200 so it doesn't get all over everything. Then put a first layer of carpet over the boards not over lapping. Then carpet wrap the bunks. The 5200 will take a week to set up so just tighten the bunks down snug. Then go back in a week and tighten again and double nut.
99 MariStar 230 Sport LTR 330