Underbody coating - Waxoyl, Dinitrol, Dynax??

[JimM169]

Daughter's Aygo has just been for it's MOT and one of the advisories that there is rust on the subframes, guy said it's not bad just needs a wire brush and a coating applied. Years ago something by Waxoyl would have been the go to stuff but guessing things might have changed in the last 30years!
What's the best product for the job these days, I'll probably give the whole underside a going over while I'm under there and try and do the inside of sills, chassis rails etc as well.
Not as nimble as I used to be so the easier to apply the better and I do have a compressor if that makes a difference

Thanks

[GreenV8S]

If it isn't currently oily then after cleaning road muck off I'd apply a coating of rust converter to the main rusty areas, then slap some underbody paint on. Mist some waxoyl over the top for extra protection.

Waxoyl and the like are something you'd apply over paint to reduce the damage from chips, not instead of paint.

[donkmeister]

There are companies who specialise in it, but not sure if you would find it a worthwhile cost in such a car.

I had an S2000 done by South West Rustproofing in the strength of a PH article. It wasn't a cheap job but it was thorough. They took out liners, steam cleaned things, injected it into things. That was a few years ago now, it's driven in all weathers, I had it up on a lift recently and it still looked great. Dinitrol was their libation of choice.

[julianm]

Bilt Hamber UC & UB are very good waxesuse for in cavities & general underbody protection.

[Belle427]

Dinitrol and Bilt Hamber are both very good so id just pick whichever was most reasonably priced.

[JimM169]

Thanks to all that replied. Managed to have a look under the car this evening and the actual bits that need sorting are much smaller than I thought. Majority of underbody has the the factory coating on and is in good nick, it's literally just the cross members that appear to be untreated and have some corrosion. So as GreenV8S suggested I'll give them a go over with the wire brush and slap some hammerite on as have a tin of that in the garage. I'll probably also grab a tin of BH Dynax S50 for the interior sections and any that's left over will be sprayed over the underbody.