What I did last year.
I commissioned a new hard-bottom inflatable last year. I sanded the f/g hull with 80-grit paper. (Ensure that you get it all.) Then I painted it with 2 coats of ablative bottom paint. I estimated the waterline on the pontoons and masked it off. I used the ablative on this portion, too (2 coats). It stood up excellent from May-October when I hauled it. I scrubbed the bottom with a whitewall brush and much of the ablative came off. I stored it, inverted, on the foredeck under the shrink wrap. I will do the same procedure this spring, only I will wash the bottom instead of sanding it.