That sucks! Yeah we only use sand here in the state of Washington. Salt is bad for our lakes and streams. So is oil and WD-40, WTF? Isn't there a thing called undercoating?
as touched on by others, hard undercoating isn't very effective long-term in fighting salt-induced rust damage. the genie is out of the bottle as far as treating the roads - people are accustomed to driving on dry pavement, and demand it. the only way to accomplish that is by applying salt-based deicers to the road surface, which have the negative effect of rusting our vehicles.
btw, protecting the chassis and bodies of vehicles IS environmentally friendly, not the other way around. by using those products yearly, i prevent my vehicles from disintegrating, which limits my demands on iron, steel, and aluminum being needed to create another vehicle from raw materials.
for more than 20 years, i had a local place apply oil undercoating to the body panels and frames of my vehicles. it was similar to bar & chain oil. pretty good adherence, absolutely protected the vehicles from rusting. the downside was that it attracted dust/dirt, so if clean looking cars are important to you, that was a battle (it isn't an issue to me). however, the cost of having the shops do it ultimately got more expensive (runs about $125 to $200 per vehicle right now). so, for the last few years, i've done it myself. for the first two years of doing it myself, i used an oil sprayer, and applied used gear oil to the frames, inner sides of the body panels, and underneath the cars/trucks.
this year, i decided to try fluid-film. i bought 16 cans of the aerosol, and it was enough to thoroughly cover all of the insides and frames of four vehicles: my '87 4runner, '91 celica, '89 camry, and '48 dodge dump truck. and the cost was less than $125 for the product. the downside was it took time to apply it to all the cars, but that's ok with me. i took the time to remove inner rocker covers to access the rockers, fender panels, etc. also popped off a few inner trim panels to get to the backsides of the bodies.
i'll see how well it does compared to the "gear oil/bar oil" treatments. i retired a '95 subaru wagon 3 years ago, which showed only limited rust, not the typical subaru rust-through that occurs to new england subies.
an added benefit to oil/fluid protection is that chassis/steering/underside parts don't get rust-welded together as readily, and often can be loosened/removed without breaking them.
pic of my subie, at the normal terrible rust-through location, at the rear struts. never did any body work to it, the pic is of the original rear quarter panel (this was in 2016, AFTER i retired it from the road, so it was a 18 year old subaru that spent its entire life in new england - i beat the snot out of it, 297K miles):
wally