Outdoor Carpet Adhesive Wrong?

Hey guys just bought some of what I think is the go-to outdoor carpet adhesive for most john boat converters but I am confused. Everyone seems to say three coats of spar varnish on marine grade plywood then carpet with adhesive. But, the can of adhesive says do not use on stained, painted, or water sealed surfaces. It also says not to use on urethane backed carpet which I'm not sure if what I have is polyurethane backed but it appears to be rubber backed. So staples?

All I can say is what I did. I used cheap in door/ outdoor carpet , adhesive for same. Pre cut carpet to fit ,apply glue with a notched trial and trimmed excess carpet. It lasted about 6 years of use and sitting uncovered in the weather.

I have 2x6 pressure treated bunks, no glue, staples only. 6 years old now also.
but, if you are sometimes in salt water, shorten the staple life quickly.

and say to yourself .... you are gluing carpet to a BOAT TRAILER !!
not a piece of furniture, not a yacht, not a piece of playground equipment.

a BOAT TRAILER !!!! just do it your way. it will work.
also, what is the worse that can happen if it doesn't ???

Don't use a spray on adhesive. It doesn't have enough strength to do the job. Use 150 grit sand paper to scuff up your spar varnished surfaces. Clean the dust off with vacuum and tack rag. Then apply a brush on or trowel on carpet glue.

Let us know how it goes.