Norm replied:

This answer about paint protection is based on personal opinion and some experience with a brand of paint protection of which I used to apply to new cars. Personally I believe it is mainly a way for the dealers to separate you from some of your hard earned moolah, folding stuff,golden eagle poo or whatever you like to refer to it as. I have applied this stuff and maybe it works for some time but I dont know how they justify the costs that they try and charge. Personally I wouldnt use it on my grandmothers shopping trolley. i believe that there is no substitute for a good brand of polish and wax and good old fashioned elbow grease.

Rob replied:

Id go for it Don. Ive been driving on the beach for 20 years & have always paided attention to the underneath & in particular the seams & the inside of panels. The rust seems to start from the inside & by the time you get to see it on the outside, it is too late. Tectyl is fine for the inside of panels & underneath. This will penertrate the seems & joins & therefore stop water sitting in there & turning to rust. I have always done the job myself using a brush & one of those hand operated sprayers, so you can get into the tight spots. Make sure you put a sheet of plastic down on the drive & wear a pair of disposable overalls. Throw a cover over the car to catch the overspray.
It always amazes me when I see steel in the outback that has been sitting there for a hundred years with a light coat of rust on it. Living a stone throw from the ocean, a layer of rust happens overnight.