I think i will use a normal spray gun to coat the underside, then try the underseal gun in the cavities.

Great bits of kit, but mine didnt work for heated dinitrol 4191 and would still need thinning unless i'm doing it wrong! For spraying the stuff above, i would just decant into an empty shutz can and use the gun as per normal. This will give you enough for rust-proofing the underbody of a small to medium sized van such as a Transporter or Bongo. The best underseal technology is now used during production and does extend the life of the underbody significantly, although does eventually chip away.

Over time the factory finish on the chasis/underside of cars improved and in the early 00’s this technology, later this was also introduced to vans. Please be sensible when you make this stuff; don't go breathing the fumes or applying heat and burning down your house. A quality rust-proofing job that stays intact close to a decade will give you the peace of mind that your vehicle is well protected despite the weather conditions. It runs nicely, it sounds great, and it looks the part - but have you done all you can to protect it? Car and van undersealing is an essential procedure for both new and used vehicles to increase their life expectancy.

The Liqui Molly underseal offers a shield against corrosion by creating a tough, protective film on the underbody. It can be done on ramps or axle stands – just make sure it’s safe before getting under the car and make sure you wear old clothes and eye protection. In fact, look in any scrapyard and you will see a surprising number of relatively modern vehicles which have succumbed to the MoT tester’s screwdriver. Access to the sills and other enclosed areas can usually be gained by carefully removing a blanking plate or grommet.I'm only using the oil on the inside of the chassis,so it won't look filthy and collect dirt,and It doesn't seem to smell any worse than usual.