update:
well ive been putting it off all summer long but i decided it was time to underseal the 350 so i went for POR15 as ive heard very good reviews about it and i must say it is amazing stuff,
but... if you have never done this before i can reveal it truly is the most horrible job you can do on a car,
but im very pleased with how it turned out there are a few bits i need to come back to total time was nearly 3 hours