If you plan to use it i would seriously research Buzzwelds chassis in one paint CIO. Its a multi stage paint that is self etching. They use it on land rovers that are going off road in all weather conditions and I have used it in the past its simply superb and although many spray it on get a gloss roller on a mini roller handle and you can generally roller most of the underside of a car and the tight bits paint with a brush.
You must clean the underside thoroughly to make sure the surface you apply it to is clean and free from dirt/grime and it goes without saying that if there is any surface corrosion you must wire brush or grind it back to bare metal too.
The CIO has a primer included in the multi later so its almost a one stop solution.
After doing this i would then once dry spray Bilt and Hamber Dynax UC all over the CIO areas you painted and allow to dry. You can use this on the subframe too its an excellent protector. The cavities in chassis rails and anywhere you spot a hole you can inject with Bilt and Hamber S50.
You can even spray your arms etc with the UC it effectively will leave a micro film clear protection on them and you would barley be able to see it unless you got very close.
This is all a lot of work but if you take the time your car during winter will stay near perfect and each year just for peace of mind you can just top up the UC and s50 it should last many many years this way.
The CIO and dynax combinations looks way better than old school wax oil(black sticky variety) and i can personally say if done properly will also likely last longer but requires a little more prep.
For best results get someone to perform the above and use a dessicant dehumidifier set to 50-55 in between coats and stages for at least 8-9 hours as this will get the products to cure and dry perfectly between coats.
That's the underside taken care off but its a Maserati so someone with more mechanical knowledge might tell you it wont prove reliable, having said that my Maserati has been reliable.
Link for Chassis in one.
BUZZWELD CIO Chassis In One Targeted at our customers who want a simple medium term 10 years estimated solution compared to our extreme 4 coat dual
www.buzzweld.co.uk
GL