Tectyl or x troll worth doing although a very messy job. Get into the main bearers as this is where rust will start unseen.you will need a Schutz Gun to get any pent ration, usually you will have holes for wiring g etc along the bearers to allow you to do sections at a time. I replaced the rigid tubing with plastic tubing and on the end used a 360 degree 4mm garden sprinkler fitting. Do it all before putting the boat on. Dont forget the roller brackets as a lot are hollowed stems.
Edit. Have had some success using a degreasing gun but could only use about 750 of tubing whereas with the Schutz Gun I could get 1.5 m of tubing.